The southwestern part of the Iranian plateau participated in the wider Ancient Near East with Elam, from the Early Bronze Age. The Persian Empire proper begins in the Iron Age, following the influx of Iranian peoples which gave rise to the Median, Achaemenid, the Parthians, the Sassanid dynasties during classical antiquity.
Once a major empire of superpower proportions, Persia as it had long been called, has been overrun frequently and has had its territory altered throughout the centuries. Invaded and occupied by Greeks, Arabs, Turks, Mongols, and others—and often caught up in the affairs of larger powers—Persia has always reasserted its national identity and has developed as a distinct political and cultural entity.
Iran is home to one of the world's oldest continuous major civilizations, with historical and urban settlements dating back to 4000 BC. The Medes unified Iran as a nation and empire in 625 BC. The Achaemenid Empire (550–330 BC) was the first of the Iranian empires to rule from the Balkans to North Africa and also Central Asia. They were succeeded by the Seleucid Empire, Parthians and Sassanids which governed Iran for almost 1,000 years.
The Islamic conquest of Persia (633–656) and the end of the Sassanid Empire was a turning point in Iranian history. Islamicization in Iran took place during 8th to 10th century and led to the eventual decline of the Zoroastrian religion in Persia. However, the achievements of the previous Persian civilizations were not lost, but were to a great extent absorbed by the new Islamic policy and civilization.
After centuries of foreign occupation and short-lived native dynasties, Iran was once again reunified as an independent state in 1501 by the Safavid dynasty who established Shi'a Islam as the official religion of their empire, marking one of the most important turning points in the history of Islam. Iran had been a monarchy ruled by a shah, or emperor, almost without interruption from 1501 until the 1979 Iranian revolution, when Iran officially became an Islamic Republic on 1 April 1979.
The earliest archaeological artifacts in Iran were found in the Kashafrud and Ganj Par sites that date back to Lower Paleolithic. Mousterian Stone tools made by Neanderthal man have also been found.There are more cultural remains of Neanderthal man dating back to the Middle Paleolithic period, which mainly have been found in the Zagros region and fewer in central Iran at sites such as Shanidar, Kobeh, Kunji, Bisetun, Tamtama, Warwasi, and Yafteh Cave. Evidence for Upper Paleolithic and Epipaleolithic periods are known mainly from the Zagros region in the caves of Kermanshah and Khoramabad and a few number of sites in the Alborz range and Central Iran.
 Neolithic to Chalcolithic
There are also 9,000 year old human and animal figurines from Teppe Sarab in Kermanshah Province among the many other ancient artifacts.In the eighth millennium BC, agricultural communities such as Chogha Bonut (the earliest village in Susiana) started to form in western Iran, either as a result of indigenous development or of outside influences. Around about the same time the earliest known clay vessels and modeled human and animal terracotta figurines were produced at Ganj Dareh, also in western Iran. The south-western part of Iran was part of the Fertile Crescent where most of humanity's first major crops were grown, in villages such as Susa (now a city still existing since 7000 BC) and settlements such as Chogha Mish, dating back to 6800 BC; there are 7,000 year old jars of wine excavated in the Zagros Mountains (now on display at The University of Pennsylvania) and ruins of 7,000 year old settlements such as Sialk are further testament to that. The two main Neolithic Iranian settlements were the Zayandeh Rud River Civilization and Ganj Dareh.
 Bronze Age
Dozens of pre-historic sites across the Iranian plateau point to the existence of ancient cultures and urban settlements in the fourth millennium BC, One of the earliest civilizations in Iranian plateau was the Jiroft Civilization in southeastern Iran, in the province of Kerman. It is one of the most artifact-rich archaeological sites in the Middle East. Archaeological excavations in Jiroft led to the discovery of several objects belonging to the fourth millennium BC, a time that goes beyond the age of civilization in Mesopotamia. There is a large quantity of objects decorated with highly distinctive engravings of animals, mythological figures, and architectural motifs. The objects and their iconography are unlike anything ever seen before by archeologists. Many are made from chlorite, a gray-green soft stone; others are in copper, bronze, terracotta, and even lapis lazuli. Recent excavations at the sites have produced the world's earliest inscription which pre-dates Mesopotamian inscriptions.
There are records of numerous ancient civilizations on the Iranian plateau before the arrival of Iranian tribes from the Pontic-Caspian steppe during the Early Iron Age. One of the main civilizations of Iran was the Elam to the east of Mesopotamia, which started from around 3000 BC. The Jiroft culture occupied southeastern Iran and may have existed as far back as 3000 BC The Early Bronze Age saw the rise of urbanization into organized city states and the invention of writing (the Uruk period) in the Near East. While Bronze Age Elam made use of writing from an early time, the Proto-Elamite script remains undeciphered, and records from Sumer pertaining to Elam are scarce.
 Early Iron Age
Records become more tangible with the rise of the Neo-Assyrian Empire and its records of incursions from the Iranian plateau. As early as the 20th century BC, tribes came to the Iranian Plateau from the Pontic-Caspian steppe .The arrival of Iranians on the Iranian plateau forced the Elamites to relinquish one area of their empire after another and to take refuge in Susiana, Khuzistan and nearby area, which only then became coterminous with Elam. By the mid 1st millennium BC, Medes, Persians, and Parthians populated the Iranian plateau.
 Classical Antiquity
 Median and Achaemenid Empire (650 BC–330 BC)
In 646 BC, The Assyrian king Ashurbanipal sacked Susa, which ended Elamite supremacy in the region. For over 150 years Assyrian kings of nearby Northern Mesopotamia were seeking to conquer Median tribes of Western Iran. Under pressure from the Assyrian empire, the small kingdoms of the western Iranian plateau coalesced into increasingly larger and more centralized states. In the second half of the 7th century BC, the Median tribes gained their independence and were united by Deioces. In 612 BC Cyaxares, Deioces' grandson, and the Babylonian king Nabopolassar invaded Assyria and laid siege to and eventually destroyed Nineveh, the Assyrian capital, which led to the fall of the Neo-Assyrian Empire. The Medes are credited with the foundation of Iran as a nation and empire, and established the first Iranian empire, the largest of its day until Cyrus the Great established a unified empire of the Medes and Persians leading to the Achaemenian Empire (648–330 BC).
Cyrus the Great overthrew, in turn, the Medes, Lydians, and Babylonians, creating an empire far larger than Assyria. He was better able, through more benign policies, to reconcile his subjects to Persian rule; and the longevity of his empire was one result. The Persian king, like the Assyrian, was also "King of Kings," xšāyaθiya xšāyaθiyānām (shāhanshāh in modern Persian) – "great king," Megas Basileus, as known by the Greeks.
Cambyses II conquered Ancient Egypt, overthrowing the Dynasty XXVI. Since he became ill and died before, or while, leaving Egypt, stories developed, as related by Herodotus, that he was struck down for impiety against the Egyptian pantheon. Be that as it may, it led to a succession crisis. The winner, Darius I of Persia, based his claim on membership in a collateral line of the Achaemenid Dynasty.
Darius' first capital was at Susa, and he started the building programme at Persepolis. He rebuilt a canal between the Nile and the Red Sea, a forerunner of the modern Suez Canal. He improved the extensive road system, and it is during his reign that mention is first made of the Royal Road (shown on map), a great highway stretching all the way from Susa to Sardis with posting stations at regular intervals. Major reforms took place under Darius. Coinage, in the form of the daric (gold coin) and the shekel (silver coin) was introduced (coinage had already been invented over a century before in Lydia ca. 660 BC), and administrative efficiency was increased. The Old Persian language appears in royal inscriptions, written in a specially adapted version of cuneiform. Under Cyrus the Great and Darius the Great, the Persian Empire eventually became the largest empire in human history up until that point, ruling and administrating over most of the then known world. Their greatest achievement was the empire itself. The Persian Empire represented the world's first superpower. that was based on a model of tolerance and respect for other cultures and religions.
In 499 BC, Athens lent support to a revolt in Miletus which resulted in the sacking of Sardis. This led to an Achaemenid campaign against Greece known as the Greco-Persian Wars which lasted the first half of the 5th century BC. During the Greco-Persian wars Persia made some major advantages and razed Athens in 480 BC, but after a string of Greek victories the Persians were forced to withdraw while losing control of Macedonia, Thrace and Ionia. Fighting ended with the peace of Callias in 449 BC. In 404 BC following the death of Darius II Egypt rebelled under Amyrtaeus. Later Egyptian Pharaohs successfully resisted Persian attempts to reconquer Egypt until 343 BC when Egypt was reconquered by Artaxerxes III.
 The Hellenic conquest and the Seleucid Empire (312 BC – 63 BC)
In 334 BC-331 BC Alexander the Great, also known in the Zoroastrian Arda Wiraz Nâmag as "the accursed Alexander", defeated Darius III in the battles of Granicus, Issus and Gaugamela, swiftly conquering the Persian Empire by 331 BC. Alexander's empire broke up shortly after his death, and Alexander's general, Seleucus I Nicator, tried to take control of Persia, Mesopotamia, and later Syria and Asia Minor. His ruling family is known as the Seleucid Dynasty. However he was killed in 281 BC by Ptolemy Keraunos. Greek language, philosophy, and art came with the colonists. During the Seleucid Dynasty throughout Alexander's former empire, Greek became the common tongue of diplomacy and literature. Overland trade brought about some fascinating cultural exchanges. Buddhism came in from India, while Zoroastrianism travelled west to influence Judaism. Incredible statues of the Buddha in classical Greek styles have been found in Persia and Afghanistan, illustrating the mix of cultures that occurred around this time (See Greco-Buddhism).
 Parthian Empire (248 BC — AD 224)
The Parthian Empire was the realm of the Arsacid dynasty, who reunited and governed the Iranian plateau after defeating the Greek Seleucid Empire in the later 3rd century BC, and intermittently controlled Mesopotamia between ca 150 BC and AD 224. This was the second native dynasty of ancient Iran (Persia).
Parthia was the Eastern arch-enemy of the Roman Empire; and it limited Rome's expansion beyond Cappadocia (central Anatolia). The Parthian armies included two types of cavalry: the heavily armed and armoured cataphracts and lightly armed but highly mobile mounted archers. For the Romans, who relied on heavy infantry, the Parthians were too hard to defeat, as both types of cavalry were much faster and more mobile than foot soldiers. On the other hand, the Parthians found it difficult to occupy conquered areas as they were unskilled in siege warfare. Because of these weaknesses, neither the Romans nor the Parthians were able completely to annex each other's territory.
The Parthian empire subsisted for five centuries, longer than most Eastern Empires. The end of this empire came at last in AD 224, when the empire's organization had loosened and the last king was defeated by one of the empire's vassal peoples, the Persians under the Sassanian dynasty.
 Sassanid Empire (224 – 651)
The first Shah of the Sassanid Empire, Ardashir I, started reforming the country both economically and militarily. The empire's territory encompassed all of today's Iran, Iraq, Armenia, Afghanistan, eastern parts of Turkey, and parts of Syria, Pakistan, Caucasia, Central Asia, India and Arabia. During Khosrau II's rule in 590–628, Egypt, Jordan, Palestine and Lebanon were also annexed to the Empire. The Sassanians called their empire Erânshahr (or Iranshahr, "Dominion of the Aryans", i.e. of Iranians).
A chapter of Iran's history followed after roughly six hundred years of conflict with the Roman Empire. During this time, the Sassanian and Romano-Byzantine armies clashed for influence in Mesopotamia, Armenia and the Levant. Under Justinian I, the war came to an uneasy peace with payment of tribute to the Sassanians. However the Sassanians used the deposition of the Byzantine Emperor Maurice as a casus belli to attack the Empire. After many gains, the Sassanians were defeated at Issus, Constantinople and finally Nineveh, resulting in peace. With the conclusion of the Roman-Persian wars, the war-exhausted Persians lost the Battle of al-Qâdisiyah (632) in Hilla, (present day Iraq) to the invading forces of Islam.
The Sassanian era, encompassing the length of the Late Antiquity period, is considered to be one of the most important and influential historical periods in Iran, and had a major impact on the world. In many ways the Sassanian period witnessed the highest achievement of Persian civilization, and constitutes the last great Iranian Empire before the adoption of Islam. Persia influenced Roman civilization considerably during Sassanian times, their cultural influence extending far beyond the empire's territorial borders, reaching as far as Western Europe, Africa, China and India and also playing a prominent role in the formation of both European and Asiatic medieval art. This influence carried forward to the Islamic world. The dynasty's unique and aristocratic culture transformed the Islamic conquest and destruction of Iran into a Persian Renaissance. Much of what later became known as Islamic culture, architecture, writing and other contributions to civilization, were taken from the Sassanian Persians into the broader Muslim world.
 Medieval Iran
 Caliphate and Sultanate era
 Islamic conquest
Muslims invaded Iran in the time of Umar (637) and conquered it after several great battles. The last Sassanid ruler, Yazdegerd III, fled from one district to another until a local miller killed him for his purse at Merv in 651. By 674, Muslims had conquered Greater Khorasan (which included modern Iranian Khorasan province and modern Afghanistan and parts of Transoxania). The Islamic conquest of Persia ended the Sassanid Empire and led to the eventual decline of the Zoroastrian religion in Persia. Over time, the majority of Iranians converted to Islam. However, most of the achievements of the previous Persian civilizations were not lost, but were absorbed by the new Islamic polity.
"These events have been variously seen in Iran: by some as a blessing, the advent of the true faith, the end of the age of ignorance and heathenism; by others as a humiliating national defeat, the conquest and subjugation of the country by foreign invaders. Both perceptions are of course valid, depending on one's angle of vision."
 Umayyad Caliphate
After the fall of Sasanian dynasty in 651, the Umayyad Arabs adopted many Persian customs especially the administrative and the court mannerisms. Arab provincial governors were undoubtedly either Persianized Arameans or ethnic Persians; certainly Persian remained the language of official business of the caliphate until the adoption of Arabic toward the end of the 7th century, when in 692 minting began at the caliphal capital, Damascus. The new Islamic coins evolved from imitations of Sassanian coins (as well as Byzantine), and the Pahlavi script on the coinage was replaced with Arabic alphabet.
During the reign of the Ummayad dynasty, the Arab conquerors imposed Arabic as the primary language of the subject peoples throughout their empire. Hajjāj ibn Yusuf, who was not happy with the prevalence of the Persian language in the divan, ordered the official language of the conquered lands to be replaced by Arabic, sometimes by force. In Biruni's From The Remaining Signs of Past Centuries for example it is written:
"When Qutaibah bin Muslim under the command of Al-Hajjaj bin Yousef was sent to Khwarazmia with a military expedition and conquered it for the second time, he swiftly killed whomever wrote the Khwarazmian native language that knew of the Khwarazmian heritage, history, and culture. He then killed all their Zoroastrian priests and burned and wasted their books, until gradually the illiterate only remained, who knew nothing of writing, and hence their history was mostly forgotten."
There are a number of historians who see the rule of the Umayyads as setting up the "dhimmah" to increase taxes from the dhimmis to benefit the Arab Muslim community financially and by discouraging conversion. Governors lodged complaints with the caliph when he enacted laws that made conversion easier, depriving the provinces of revenues.
In the 7th century AD, when many non-Arabs such as Persians entered Islam were recognized as Mawali and treated as second class citizens by the ruling Arab elite, until the end of the Umayyad dynasty. During this era Islam was initially associated with the ethnic identity of the Arab and required formal association with an Arab tribe and the adoption of the client status of mawali. The half-hearted policies of the late Umayyads to tolerate non-Arab Muslims and Shi'as had failed to quell unrest among these minorities. If this was the case, this practice went against the teachings of Islam because the Prophet Madinah had a close companion named Salman the Persian. With the death of the Umayyad Caliph Hisham ibn Abd al-Malik in 743, the Islamic world was launched into civil war. Abu Muslim was sent to Khorasan by the Abbasids initially as a propagandist and then to revolt on their behalf. He took Merv defeating the Umayyad governor there Nasr ibn Sayyar. He became the de facto Abbasid governor of Khurasan. In 750, Abu Muslim became leader of the Abbasid army and defeated the Umayyads at the Battle of the Zab. Abu Muslim stormed Damascus, the capital of the Umayyad caliphate, later that year.
 Abbasid Caliphate and Iranian semi-independent governments
The Abbasid army consisted primarily of Khorasanians and was led by an Iranian general, Abu Muslim Khorasani. It contained both Iranian and Arab elements, and the Abbasids enjoyed both Iranian and Arab support. The Abbasids overthrew the Umayyads in 750.
One of the first changes the Abbasids made after taking power from the Umayyads was to move the empire's capital from Damascus, in Levant, to Iraq. The latter region was influenced by Persian history and culture, and moving the capital was part of the Persian mawali demand for Arab influence in the empire. The city of Baghdad was constructed on the Tigris River, in 762, to serve as the new Abbasid capital. The Abbasids established the position of vizier like Barmakids in their administration, which was the equivalent of a "vice-caliph", or second-in-command. Eventually, this change meant that many caliphs under the Abbasids ended up in a much more ceremonial role than ever before, with the vizier in real power. A new Persian bureaucracy began to replace the old Arab aristocracy, and the entire administration reflected these changes, demonstrating that the new dynasty was different in many ways to the Umayyads.
By the 9th century, Abbasid control began to wane as regional leaders sprang up in the far corners of the empire to challenge the central authority of the Abbasid caliphate. The Abbasid caliphs began enlisting Turkic-speaking warriors who had been moving out of Central Asia into Transoxiana as slave warriors as early as the ninth century. Shortly thereafter the real power of the Abbasid caliphs began to wane; eventually they became religious figureheads while the warrior slaves ruled. As the power of the Abbasid caliphs diminished, a series of dynasties rose in various parts of Iran, some with considerable influence and power. Among the most important of these overlapping dynasties were the Tahirids in Khorasan (820–72); the Saffarids in Sistan (867–903); and the Samanids (875–1005), originally at Bokhara. The Samanids eventually ruled an area from central Iran to Pakistan. By the early 10th century, the Abbasids almost lost control to the growing Persian faction known as the Buwayhid dynasty (934–1055). Since much of the Abbasid administration had been Persian anyway, the Buwayhid were quietly able to assume real power in Baghdad. The Buwayhid were defeated in the mid-11th century by the Seljuq Turks, who continued to exert influence over the Abbasids, while publicly pledging allegiance to them. The balance of power in Baghdad remained as such – with the Abbasids in power in name only – until the Mongol invasion of 1258 sacked the city and definitively ended the Abbasid dynasty.
During the Abbassid period an enfranchisement was experienced by the mawali and a shift was made in political conception from that of a primarily Arab empire to one of a Muslim empire and c. 930 a requirement was enacted that required all bureaucrats of the empire be Muslim.
 Islamic golden age, Shu'ubiyya movement and Persianization process
Richard Bulliet's "conversion curve" indicates that only about 10% of Iran converted to Islam during the relatively Arab-centric Umayyad period. Beginning in the Abassid period, with its mix of Persian as well as Arab rulers, the Muslim percentage of the population rose. As Persian Muslims consolidated their rule of the country, the Muslim population rose from approx. 40% in the mid 9th century to close to 100% by the end of 11th century. Seyyed Hossein Nasr suggests that the rapid increase in conversion was aided by the Persian nationality of the rulers.
Although Persians adopted the religion of their conquerors, over the centuries they worked to protect and revive their distinctive language and culture, a process known as Persianization. Arabs and Turks participated in this attempt.
In the 9th and 10th centuries, non-Arab subjects of the Ummah created a movement called Shu'ubiyyah in response to the privileged status of Arabs. Most of those behind the movement were Persian, but references to Egyptians, Berbers and Aramaeans are attested. Citing as its basis Islamic notions of equality of races and nations, the movement was primarily concerned with preserving Persian culture and protecting Persian identity, though within a Muslim context. The most notable effect of the movement was the survival of the Persian language to the present day.
The Samanid dynasty led the revival of Persian culture and the first important Persian poet after the arrival of Islam, Rudaki, was born during this era and was praised by Samanid kings. The Samanids also revived many ancient Persian festivals. Their successor, the Ghaznawids, who were of non-Iranian Turkic origin, also became instrumental in the revival of Persian.
The culmination of the Persianization movement was the Shahname, the national epic of Iran, written almost entirely in Persian. This voluminous work, reflects Iran's ancient history, its unique cultural values, its pre-islamic Zoroastrian religion, and its sense of nationhood.
"Iran was indeed Islamized, but it was not Arabized. Persians remained Persians. And after an interval of silence, Iran reemerged as a separate, different and distinctive element within Islam, eventually adding a new element even to Islam itself. Culturally, politically, and most remarkable of all even religiously, the Iranian contribution to this new Islamic civilization is of immense importance. The work of Iranians can be seen in every field of cultural endeavor, including Arabic poetry, to which poets of Iranian origin composing their poems in Arabic made a very significant contribution. In a sense, Iranian Islam is a second advent of Islam itself, a new Islam sometimes referred to as Islam-i Ajam. It was this Persian Islam, rather than the original Arab Islam, that was brought to new areas and new peoples: to the Turks, first in Central Asia and then in the Middle East in the country which came to be called Turkey, and of course to India. The Ottoman Turks brought a form of Iranian civilization to the walls of Vienna..."
The Islamization of Iran was to yield deep transformations within the cultural, scientific, and political structure of Iran's society: The blossoming of Persian literature, philosophy, medicine and art became major elements of the newly forming Muslim civilization. Inheriting a heritage of thousands of years of civilization, and being at the "crossroads of the major cultural highways", contributed to Persia emerging as what culminated into the "Islamic Golden Age". During this period, hundreds of scholars and scientists vastly contributed to technology, science and medicine, later influencing the rise of European science during the Renaissance.
The most important scholars of almost all of the Islamic sects and schools of thought were Persian or live in Iran including most notable and reliable Hadith collectors of Shia and Sunni like Shaikh Saduq, Shaikh Kulainy, Imam Bukhari, Imam Muslim and Hakim al-Nishaburi, the greatest theologians of Shia and Sunni like Shaykh Tusi, Imam Ghazali, Imam Fakhr al-Razi and Al-Zamakhshari, the greatest physicians, astronomers, logicians, mathematicians, metaphysicians, philosophers and scientists like Al-Farabi, Avicenna, and Nasīr al-Dīn al-Tūsī, the greatest Shaykh of Sufism like Rumi, Abdul-Qadir Gilani.
 Turco-Persian dynasties
In 962 a Turkish governor of the Samanids, Alptigin, conquered Ghazna (in present-day Afghanistan) and established a dynasty, the Ghaznavids, that lasted to 1186. The Ghaznavid empire grew by taking all of the Samanid territories south of the Amu Darya in the last decade of the 10th century, and eventually occupied much of present-day Iran, Afghanistan, Pakistan and northwest India. The Ghaznavids are generally credited with launching Islam into Hindu-dominated India. The invasion of India was undertaken in 1000 by the Ghaznavid ruler, Mahmud, and continued for several years. They were unable to hold power for long, however, particularly after the death of Mahmud in 1030. By 1040 the Seljuqs had taken over the Ghaznavid lands in Iran.
The Seljuqs, who like the Ghaznavids were Turks, slowly conquered Iran over the course of the 11th century. The dynasty had its origins in the Turcoman tribal confederations of Central Asia and marked the beginning of Turkic power in the Middle East. They established a Sunni Muslim dynasty that ruled parts of Central Asia and the Middle East from the 11th to 14th centuries. They set up an empire known as Great Seljuq Empire that stretched from Anatolia in the west to western Afghanistan in the east and the western borders of (modern-day) China in the northeast; and was the target of the First Crusade. Today they are regarded as the cultural ancestors of the Western Turks, the present-day inhabitants of Azerbaijan, Turkey, and Turkmenistan, and they are remembered as great patrons of Persian culture, art, literature, and language. Their leader, Tughril Beg, turned his warriors against the Ghaznavids in Khorasan. He moved south and then west, conquering but not wasting the cities in his path. In 1055 the caliph in Baghdad gave Tughril Beg robes, gifts, and the title King of the East. Under Tughril Beg's successor, Malik Shah (1072–1092), Iran enjoyed a cultural and scientific renaissance, largely attributed to his brilliant Iranian vizier, Nizam al Mulk. These leaders established the observatory where Omar Khayyám did much of his experimentation for a new calendar, and they built religious schools in all the major towns. They brought Abu Hamid Ghazali, one of the greatest Islamic theologians, and other eminent scholars to the Seljuq capital at Baghdad and encouraged and supported their work.
When Malik Shah I died in 1092, the empire split as his brother and four sons quarrelled over the apportioning of the empire among themselves. In Anatolia, Malik Shah I was succeeded by Kilij Arslan I who founded the Sultanate of Rûm and in Syria by his brother Tutush I. In Persia he was succeeded by his son Mahmud I whose reign was contested by his other three brothers Barkiyaruq in Iraq, Muhammad I in Baghdad and Ahmad Sanjar in Khorasan. As Seljuq power in Iran weakened, other dynasties began to step up in its place, including a resurgent Abbasid caliphate and the Khwarezmshahs. The Khwarezmid Empire was a Sunni Muslim dynasty that ruled in Central Asia. Originally vassals of the Seljuqs, they took advantage of the decline of the Seljuqs to expand into Iran. In 1194 the Khwarezmshah Ala ad-Din Tekish defeated the Seljuq sultan Toghrul III in battle and the Seljuq empire in Iran collapsed. Of the former Seljuq Empire, only the Sultanate of Rüm in Anatolia remained.
A serious internal threat to the Seljuqs during their reign came from the Ismailis, a secret sect with headquarters at Alamut between Rasht and Tehran. They controlled the immediate area for more than 150 years and sporadically sent out adherents to strengthen their rule by murdering important officials. Several of the various theories on the etymology of the word assassin derive from these killers.
 Mongols, Timurids and local governments
The Khwarezmid Empire only lasted for a few decades, until the arrival of the Mongols. Genghis Khan had unified the Mongols, and under him the Mongol Empire quickly expanded in several directions, until by 1218 it bordered Khwarezm. At that time, the Khwarezmid Empire was ruled by Ala ad-Din Muhammad (1200–1220). Muhammad, like Genghis, was intent on expanding his lands and had gained the submission of most of Iran. He declared himself shah and demanded formal recognition from the Abbasid caliph an-Nasir. When the caliph rejected his claim, Ala ad-Din Muhammad proclaimed one of his nobles caliph and unnsuccessfully tried to depose an-Naisr.
The Mongol invasion of Iran began in 1219, after two diplomatic missions to Khwarezm sent by Genghis Khan had been massacred. During 1220–21 Bukhara, Samarkand, Herat, Tus, and Nishapur were razed, and the whole populations were slaughtered. The Khwarezm-Shah fled, to die on an island off the Caspian coast. Before his death in 1227, Genghis had reached western Azarbaijan, pillaging and burning cities along the way.
The Mongol invasion was disastrous to the Iranians. Although the Mongol invaders were eventually converted to Islam and accepted the culture of Iran, the Mongol destruction of the Islamic heartland marked a major change of direction for the region. Much of the six centuries of Islamic scholarship, culture, and infrastructure was destroyed as the invaders burned libraries, and replaced mosques with Buddhist temples. The Mongols killed many civilians. Just in Merv and Urgench(Gorganj) about 2.5 million civilians were slaughtered.[verification needed] Destruction of qanat irrigation systems destroyed the pattern of relatively continuous settlement, producing numerous isolated oasis cities in a land where they had previously been rare. A large number of people, particularly males, were killed; between 1220 and 1258, the total population of Iran may have dropped from 2,500,000 to 250,000 as a result of mass extermination and famine.
After Genghis' death, Iran was ruled by several Mongol commanders. Genghis' grandson, Hulagu Khan, was tasked with expanding the Mongol empire in Iran in 1255. Arriving with an army, he established himself in the region and founded the Ilkhanate, which would rule Iran for the next eighty years. He seized Baghdad in 1258 and put the last Abbasid caliph to death. The westward advance of his forces was stopped by the Mamelukes, however, at the Battle of Ain Jalut in Palestine in 1260. Hulagu's campaigns against the Muslims also enraged Berke, khan of the Golden Horde and a convert to Islam. Hulagu and Berke fought against each other, demonstrating the weakening unity of the Mongol empire.
The rule of Hulagu's great-grandson, Ghazan Khan (1295–1304) saw the establishment of Islam as the state religion of the Ilkhanate. Ghazan and his famous Iranian vizier, Rashid al-Din, brought Iran a partial and brief economic revival. The Mongols lowered taxes for artisans, encouraged agriculture, rebuilt and extended irrigation works, and improved the safety of the trade routes. As a result, commerce increased dramatically. Items from India, China, and Iran passed easily across the Asian steppes, and these contacts culturally enriched Iran. For example, Iranians developed a new style of painting based on a unique fusion of solid, two-dimensional Mesopotamian painting with the feathery, light brush strokes and other motifs characteristic of China. After Ghazan's nephew Abu Said died in 1335, however, the Ilkhanate lapsed into civil war and was divided between several petty dynasties – most prominently the Jalayirids, Muzaffarids, Sarbadars and Kartids.
Iran remained divided until the arrival of Timur, who is variously described as of Mongol or Turkic origin. After establishing a power base in Transoxiana, he invaded Iran in 1381 and conquered it piece by piece. Timur's campaigns were known for their brutality; many people were slaughtered and several cities were destroyed. His regime was characterized by its inclusion of Iranians in administrative roles and its promotion of architecture and poetry. His successors, the Timurids, maintained a hold on most of Iran until 1452, when they lost the bulk of it to Black Sheep Turkmen. The Black Sheep Turkmen were conquered by the White Sheep Turkmen under Uzun Hasan in 1468; Uzun Hasan and his successors were the masters of Iran until the rise of the Safavids.
 Sunnism and Shiism in pre-Safavid Iran
Sunnism was dominant form of Islam in most part of Iran from the beginning until rise of Safavids empire. Sunni Islam was more than 90% of population of Persia before the Safavids. According to Mortaza Motahhari the majority of Iranian scholars and masses remained Sunni till the time of the Safavids. The domination of Sunnis did not mean Shia were rootless in Iran. The writers of The Four Books of Shia were Iranian, as well as many other great Shia scholars.
The domination of the Sunni creed during the first nine Islamic centuries characterized the religious history of Iran during this period. There were however some exceptions to this general domination which emerged in the form of the Zaydīs of Tabaristan, the Buwayhid, the rule of Sultan Muhammad Khudabandah (r. Shawwal 703-Shawwal 716/1304-1316) and the Sarbedaran. Apart from this domination there existed, firstly, throughout these nine centuries, Shia inclinations among many Sunnis of this land and, secondly, original Imami Shiism as well as Zaydī Shiism had prevalence in some parts of Iran. During this period, Shia in Iran were nourished from Kufah, Baghdad and later from Najaf and Hillah. Shiism were dominant sect in Tabaristan, Qom, Kashan, Avaj and Sabzevar. In many other areas merged population of Shia and Sunni lived together.
During the 10th and 11th centuries, Fatimids sent Ismailis Da'i (missioners) to Iran as well as other Muslim lands. When Ismailis divided into two sects, Nizaris established their base in Iran. Hassan-i Sabbah conquered fortresses and captured Alamut in 1090 AD. Nizaris used this fortress until a Mongol raid in 1256.
After the Mongol raid and fall of the Abbasids, Sunni hierarchies faltered. Not only did they lose the caliphate but also the status of official madhab. Their loss was the gain of Shia, whose center wasn't in Iran at that time. Several local Shia dynasties like Sarbadars were established during this time.
The main change occurred in the beginning of the 16th century, when Ismail I founded the Safavid dynasty and initiated a religious policy to recognize Shi'a Islam as the official religion of the Safavid Empire, and the fact that modern Iran remains an officially Shi'ite state is a direct result of Ismail's actions.
 Early modern era
Persia underwent a revival under the Safavid dynasty (1502–1736), the most prominent figure of which was Shah Abbas I. Some historians credit the Safavid dynasty for founding the modern nation-state of Iran. Iran's contemporary Shia character, and significant segments of Iran's current borders take their origin from this era (e.g. Treaty of Zuhab).
 Safavid Empire (1502–1736)
The Safavids were an Iranian Shia dynasty of mixed Azeri and Kurdish origins, which ruled Persia from 1501/1502 to 1722. Safavids established the greatest Iranian empire since the Islamic conquest of Persia, and established the Ithnāʻashari school of Shi'a Islam as the official religion of their empire.
The Safavid ruling dynasty was founded by Ismāil, from now known as Shāh Ismāil I. Practically worshipped by his Qizilbāsh followers, Ismāil invaded Shirvan and avenged the death of his father. Afterwards, he went on a conquest campaign, capturing Tabriz in July 1501, where he enthroned himself the Shāh of Azerbaijan and minted coins in his name, proclaiming Shi'ism the official religion of his domain. Although initially the masters of Azerbaijan only, the Safavids had, in fact, won the struggle for power in Persia which had been going on for nearly a century between various dynasties and political forces. A year after his victory in Tabriz, Ismāil proclaimed most of Persia as his domain. He soon conquered and unified Iran under his rule. Soon after, the new Safavid Empire conquered most of the modern day Afghanistan and Iraq.
The greatest of the Safavid monarchs, Shah Abbas I the Great (1587–1629) came to power in 1587 aged 16. Abbas I first fought the Uzbeks, recapturing Herat and Mashhad in 1598. Then he turned against the Ottomans, recapturing Baghdad, eastern Iraq and the Caucasian provinces by 1622. He also used his new force to dislodge the Portuguese from Bahrain (1602) and the English navy from Hormuz (1622), in the Persian Gulf (a vital link in Portuguese trade with India). He expanded commercial links with the English East India Company and the Dutch East India Company. Thus Abbas I was able to break the dependence on the Qizilbash for military might and therefore was able to centralize control. The Safavid dynasty soon became a major power in the world and started the promotion of tourism in Iran. Under their rule Persian Architecture flowered again and saw many new monuments.
Except for Shah Abbas II, the Safavid rulers after Abbas I were ineffectual. The end of his reign, 1666, marked the beginning of the end of the Safavid dynasty. Despite falling revenues and military threats, later shahs had lavish lifestyles. Shah Soltan Hosain (1694–1722) in particular was known for his love of wine and disinterest in governance. The country was repeatedly raided on its frontiers. Finally, Ghilzai Pashtun chieftain named Mir Wais Khan began a rebellion in Kandahar and defeated the Safavid army. Later, in 1722 an Afghan army led by Mir Wais' son Mahmud marched across eastern Iran, besieged, and sacked Isfahan. Mahmud proclaimed himself 'Shah' of Persia. Meanwhile, Persia's imperial rivals, the Ottomans and the Russians, took advantage of the chaos in the country to seize territory for themselves.
 Nader Shah and his successors
Iran's territorial integrity was restored by an Afshar warlord from Khorasan, Nader Shah. He defeated the Afghans and Ottomans, reinstalled the Safavids on the throne and negotiated Russian withdrawal. By 1736, Nader had become so powerful he was able to depose the Safavids and have himself crowned shah. Nader was one of the last great conquerors of Asia and his military reforms enabled his army to take Kandahar and invade Mughal India, sacking Delhi in 1739. But the increasing cruelty and oppressiveness of his later years provoked multiple revolts and, ultimately, Nader's assassination in 1747.
Nader's death was followed by a period of anarchy in Iran as rival army commanders fought for power. Nader's own family, the Afsharids, were soon reduced to holding on to a small domain in Khorasan. Ahmad Shah Durrani founded an independent state which became modern Afghanistan. From his capital Shiraz, Karim Khan of the Zand dynasty ruled "an island of relative calm and peace in an otherwise bloody and destructive period." His death in 1779 led to yet another civil war in which the Qajar dynasty eventually triumphed and became shahs of Iran.
 Qajar dynasty (1796–1925)
By the 17th century, European countries, including Great Britain, Imperial Russia, and France, had already started establishing colonial footholds in the region. Iran as a result lost sovereignty over many of its provinces to these countries via the Treaty of Turkmenchay, the Treaty of Gulistan, and others.
The Great Persian Famine of 1870–1871 is believed to have caused the death of 2 million persons.
A new era in the History of Persia dawned with the Constitutional Revolution of Iran against the Shah in the late 19th and early 20th century. The Shah managed to remain in power, granting a limited constitution in 1906 (making the country a constitutional monarchy). The first Majlis (parliament) was convened on October 7, 1906.
The discovery of oil in 1908 by the British in Khuzestan spawned intense renewed interest in Persia by the British Empire (see William Knox D'Arcy and Anglo-Iranian Oil Company, now BP). Control of Persia remained contested between the United Kingdom and Russia, in what became known as The Great Game, and codified in the Anglo-Russian Convention of 1907, which divided Persia into spheres of influence, regardless of her national sovereignty.
During World War I, the country was occupied by British and Russian forces but was essentially neutral (see Persian Campaign). In 1919, after the Russian revolution and their withdrawal, Britain attempted to establish a protectorate in Iran, which was unsuccessful.
Finally, the Constitutionalist movement of Gilan and the central power vacuum caused by the instability of the Qajar government resulted in the rise of Reza Shah Pahlavi and the establishment of the Pahlavi dynasty in 1925.
In 1921, a military coup established Reza Khan, a Persian officer of the Persian Cossack Brigade, as the dominant figure for the next 20 years. Seyyed Zia'eddin Tabatabai was also a leader and important figure in the perpetration of the coup. The Iranian coup of 1921 was not actually directed at the Qajar monarchy; according to Encyclopædia Iranica, it was targeted at officials who were in power and actually had a role in controlling the government; the cabinet and others who had a role in governing Persia. In 1925, after being prime minister for a couple of years, Reza Shah became the king of Iran and established the Pahlavi dynasty.
 Pahlavi era (1925–1979)
Reza Shah ruled for almost 16 years until September 16, 1941, when he was forced to abdicate by the Anglo-Soviet invasion of Iran. He established an authoritarian government that valued nationalism, militarism, secularism and anti-communism combined with strict censorship and state propaganda. Reza Shah introduced many socio-economic reforms, reorganizing the army, government administration, and finances. To his supporters his reign brought "law and order, discipline, central authority, and modern amenities – schools, trains, buses, radios, cinemas, and telephones". However, his attempts of modernisation have been criticised for being "too fast" and "superficial", and his reign a time of "oppression, corruption, taxation, lack of authenticity" with "security typical of police states."
In particular he clashed with Iran's clergy and devout Muslims. His laws and regulations required mosques to use chairs, all Iranian except qualifying Shia jurisconsults to wear western clothes including a hat with a brim, encouraged women to discard hijab, allowed mixing of the sexes. In 1935 bazaaris and villagers rose up in rebellion at the Imam Reza shrine in Mashhad, chanting slogans such as 'The Shah is a new Yezid.' Dozens were killed and hundreds were injured when troops finally quelled the unrest.
 World War II
Reza Shah's son Mohammad Reza Shah Pahlavi, came to power during World War II, when British and Indian forces from Iraq and Soviet forces from the north occupied Iran in August 1941. Iran was a vital oil-supply source and link in the Allied supply line for lend-lease supplies. Reza Shah was forced to abdicate in favour of his pro-British son Mohammad Reza Shah Pahlavi, who ruled until 1979.
At the Tehran Conference of 1943, the Tehran Declaration guaranteed the post-war independence and boundaries of Iran. However, when the war actually ended, Soviet troops stationed in northwestern Iran not only refused to withdraw but backed revolts that established short-lived, pro-Soviet separatist national states in the northern regions of Azerbaijan and Iranian Kurdistan, the Azerbaijan People's Government and the Republic of Kurdistan respectively, in late 1945.
Soviet troops did not withdraw from Iran proper, until May 1946 after receiving a promise of oil concessions. The Soviet republics in the north were soon overthrown and the oil concessions were revoked.
 Mohammad-Reza Shah
Initially there were hopes that post-occupation Iran could become a constitutional monarchy. The new, young Shah Mohammad Reza Shah Pahlavi initially took a very hands-off role in government, and allowed parliament to hold a lot of power. Some elections were held in the first shaky years, although they remained mired in corruption. Parliament became chronically unstable, and from the 1947 to 1951 period Iran saw the rise and fall of six different prime ministers.
In 1951 Prime Minister Mohammed Mosaddeq received the vote required from the parliament to nationalize the British-owned oil industry, in a situation known as the Abadan Crisis. Despite British pressure, including an economic blockade, the nationalization continued. Mossadegh was briefly removed from power in 1952 but was quickly re-appointed by the shah, due to a popular uprising in support of the premier and he, in turn, forced the Shah into a brief exile in August 1953 after a failed military coup by Imperial Guard Colonel Nematollah Nassiri. Shortly thereafter on August 19 a successful coup was headed by retired army general Fazlollah Zahedi, organized by the American (CIA) with the active support of the British (MI6) (known as Operation Ajax). The coup — with a black propaganda campaign designed to turn the population against Mossadegh — forced Mossadegh from office, and was remembered with anger by Iranians. Mossadegh was arrested and tried for treason. Found guilty, his sentence reduced to house arrest on his family estate while his foreign minister, Hossein Fatemi, was executed. Zahedi succeeded him as prime minister, and suppressed opposition to the Shah, specifically the National Front and Communist Tudeh Party.
Iran was ruled as an autocracy under the shah with American support from that time until the revolution. The Iranian entered into agreement with an international consortium of foreign companies which ran the Iranian oil facilities for the next 25 years splitting profits fifty-fifty with Iran but not allowing Iran to audit their accounts or have members on their board of directors. In 1957 martial law was ended after 16 years and Iran became closer to the West, joining the Baghdad Pact and receiving military and economic aid from the US. In 1961, Iran initiated a series of economic, social, agrarian and administrative reforms to modernize the country that became known as the Shah's White Revolution.
The core of this program was land reform. Modernization and economic growth proceeded at an unprecedented rate, fueled by Iran's vast petroleum reserves, the third-largest in the world. However the reforms, including the White Revolution, did not greatly improve economic conditions and the liberal pro-Western policies alienated certain Islamic religious and political groups. In early June 1963 several days of massive rioting in support of Ayatollah Ruhollah Khomeini following the clerics arrested for a speech attacking the shah.
Two year later, premier Hassan Ali Mansur was assassinated and the internal security service, SAVAK, became more violently active. In the 1970s leftist guerilla groups such as Mujaheddin-e-Khalq (MEK), emerged and attacked regime and foreign targets.
Nearly a hundred Iran political prisoners were killed by the SAVAK during the decade before the revolution and many more were arrested and tortured. The Islamic clergy, headed by the Ayatollah Ruhollah Khomeini (who had been exiled in 1964), were becoming increasingly vociferous.
Iran greatly increased its defense budget and by the early 1970s was the region's strongest military power. International relations with its neighbor Iraq were not good, mainly due to a dispute over the Shatt al-Arab waterway. In November, 1971 Iranian forces seized control of three islands at the mouth of the Persian Gulf; in response Iraq expelled thousands of Iranian nationals. Following a number of clashes in April, 1969, Iran abrogated the 1937 accord and demanded a renegotiation.
In mid-1973, the Shah returned the oil industry to national control. Following the Arab-Israeli War of October 1973, Iran did not join the Arab oil embargo against the West and Israel. Instead it used the situation to raise oil prices, using the money gained for modernization and to increase defense spending.
A border dispute between Iraq and Iran was resolved with the signing of the Algiers Accord on March 6, 1975.