The history of Iran covers thousands of years, from the kingdom of Elam to the modern Islamic Republic of Iran.

Ancient history
The ancient nation of Iran was historically known to the West as Persia until March 21, 1935. The name was used in the West due to the ancient Greek name for Iran, Persis. Persia is used to describe the nation of Iran, its people, or its ancient empire. Iranians have always called their country Iran.
The name Persia comes from a province in the south of Iran, called Fars in the modern Persian language and Pars in Middle Persian. Persis is the Hellenized form of Pars, based on which other European nations termed it Persia. This province was the core of the original Persian Empire. Westerners referred to the state as Persia until March 21, 1935, when Reza Shah Pahlavi formally asked the international community to call the country by its native name, Iran, which means Land of the Aryans. For the geography of Fars/Persia, see Geography of Iran.
Once a major empire of superpower proportions, Iran has been overrun frequently and has had its territory altered throughout the centuries. Invaded by Arabs, Turks, Mongols, and others -- and often caught up in the affairs of larger powers -- Iran has always reasserted its national identity and has developed as a distinct political and cultural entity.
Archeological findings place knowledge of Iranian prehistory at middle paleolithic times (100,000 years ago). The earliest sedentary cultures date from 18,000-14,000 years ago. The sixth millennium BC saw a fairly sophisticated agricultural society and proto-urban population centers. 7000 year old jars of wine excavated in Iran are now on display at The University of Pennsylvania.
Archeological findings place knowledge of Iranian prehistory at middle paleolithic times (100,000 years ago). The earliest sedentary cultures date from 18,000-14,000 years ago. The sixth millennium BC saw a fairly sophisticated agricultural society and proto-urban population centers. 7000 year old jars of wine excavated in Iran are now on display at The University of Pennsylvania.
Many dynasties have ruled Iran throughout the ages. Scholars and archeologists are only beginning to discover the scope of the independent, non-Semitic Elamite Empire and Jiroft civilizations  5000 years ago, many of which built ziggurats and cities before the Greek and Egyptian states came into being. At the end of second millennium, nomads from central Asia settled in Iran.
The first true empire of global proportions of Persia blossomed under the Achaemenids in (559 - 330 BC). The dynasty was founded by Cyrus the Great, who merged the various tribes and kingdoms into one unified entity. Following the Hellenistic period (300 - 250 BC) came the Parthian (250 BC - AD 226 ) and the Sassanid (226 - 651) dynasties.

Islamic Conquest
The Middle Ages
Iran's next ruling dynasties descended from Central Asian Turkic-speaking warriors who had been moving out of Central Asia into Transoxiana for more than a millennium. The Abbasid caliphs began enlisting these people 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 independent and indigenous 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 (820-872); the Saffarids in Sistan (867-903); and the Samanids (875-1005), originally at Bukhara. The Samanids eventually ruled an area from central Iran to India. In 962 a Turkish slave governor of the Samanids, Aluptigin, conquered Ghazna (in present-day Afghanistan) and established a dynasty, the Ghaznavids, that lasted to 1186.
Several Samanid cities had been lost to another Turkish group, the Seljuks, a clan of the Oghuz (or Ghuzz) Turks, who lived north of the Oxus River (present-day Amu Darya). 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 Khayyam 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 Seljuk capital at Baghdad and encouraged and supported their work.
Several Samanid cities had been lost to another Turkish group, the Seljuks, a clan of the Oghuz (or Ghuzz) Turks, who lived north of the Oxus River (present-day Amu Darya). 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 Khayyam 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 Seljuk capital at Baghdad and encouraged and supported their work.
A serious internal threat to the Seljuks, however, 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. The word assassins, which was applied to these murderers, developed from a European corruption of the name applied to them in Syria, hashishiyya, because folklore had it that they smoked hashish before their missions.

Before the First World War

Iran underwent a revival under the Safavid dynasty (1502-1736), the most prominent figure of which was Shah Abbas I. The conqueror Nadir Shah and his successors were followed by the Zand dynasty, founded by Karim Khan, and later the Qajar (1795-1925) and the Pahlavi dynasties (1925-1979).
By the 17th century, European countries, including Portugal, 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 Turkmanchai treaty, Gulistan Treaty, and others.
Modern Iranian history began with a nationalist uprising against the Shah (who remained in power) in 1905, the granting of a limited constitution in 1906 (making the country a constitutional monarchy), and the discovery of oil in 1908. The first Majlis (parliament) was convened on October 7, 1906. The key to the region was the British discovery of oil, see William Knox D'Arcy and British Petroleum. Control of the region was disputed between the United Kingdom and Russia, codified in an agreement of 1907 dividing the region into spheres of influence.

World Wars

During World War I the country was occupied by British and Russian forces but was essentially neutral. In 1919, Britain attempted to establish a protectorate in Iran, aided by the Soviet Union's withdrawal in 1921. In that year a military coup established Reza Khan, an Iranian officer of the Persian Cossack Brigade, as dictator and then hereditary Shah of the new Pahlavi dynasty (1925). Reza Shah Pahlavi ruled for almost 16 years, installed the new Pahlavi dynasty, thwarted the British attempt at control, and pushed to have the country developed.
Under his reign, Iran began to modernize and to secularize politics, and the central government reasserted its authority over the tribes and provinces.
During World War II, Iran was a vital link in the Allied supply line for lend-lease supplies to the Soviet Union. In August, 1941, British and Indian forces from Iraq and Soviet forces from the north occupied Iran. In September Reza abdicated in favour of his son Muhammad 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 did end, Soviet troops stationed in northwestern Iran not only refused to withdraw but backed revolts that established short-lived, pro-Soviet separatist regimes in the northern regions of Azerbaijan and Kurdistan, the People's Republic of Azerbaijan and the Kurdish People's Republic in late 1945, both effective Soviet puppet regimes.
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.

United States and the Shah

Several U.S. administrations, beginning in 1953 with a CIA-engineered coup to oust Prime Minister Mohammed Mossadegh and bring back Shah Mohammad Reza Pahlavi from a brief exile in Rome, to the U.S. betrayal of the shah in 1978, interfered directly in the country's internal affairs.
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 Mohammad Mossadegh, a militant nationalist, forced the parliament to nationalize the British-owned oil industry, in a situation known as the Abadan Crisis. Despite British pressure, including a economic blockade which caused real hardship, the nationalization continued. Mossadegh was briefly forced from power in 1952 but quickly returned and forced the Shah to flee. It was assumed Mossadegh would declare a republic, but a few days later the Shah returned and again forced Mossadegh from office on August 19 with U.S. CIA support. Mossadegh was arrested and a new prime minister was appointed.
In return for the US support the Shah agreed, in 1954, to allow an international consortium of British (40%), American (40%), French (6%), and Dutch (14%) companies to run the Iranian oil facilities for the next 25 years, with profits shared equally. In other words, no control or profits went to Iran. There was a return to stability in the late 1950s and the 1960s. 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. The Iranian government began a broad program of reforms to modernize the country, notably changing the quasi-feudal land system.
However the reforms did not greatly improve economic conditions and the liberal pro-Western policies alienated certain Islamic religious and political groups. From the mid-1960s the political situation was becoming increasingly unstable, with organisations such as Mujaheddin-e-Khalq (MEK) emerging. In 1961, Iran initiated a series of economic, social, and administrative reforms 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.
The Premier Hassan Ali Mansur was assassinated in 1965 and the internal security service, SAVAK, became more violently active. It is estimated that 13,000-13,500 people were killed by the SAVAK during this period of time, and thousands more were arrested and tortured. The Islamic clergy, headed by the Ayatollah Ruhollah Khomeini (who had been exiled in 1964), were becoming increasingly vociferous.
Internationally relations with Iraq fell into a steep decline, mainly due to a dispute over the Shatt-al-Arab waterway which a 1937 agreement gave to Iraq. Following a number of clashes in April, 1969, Iran abrogated the 1937 accord and demanded a renegotiation. Iran greatly increased its defense budget and by the early 1970s was the region's strongest military power. In November, 1971 Iranian forces seized control of three islands at the mouth of the Persian Gulf, in response Iraq expelling thousands of Iranian nationals.
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.
In the early 1970s, the Mujaheddin-e-Khalq organisation assassinated Tehran-based US military personnel and US civilians involved in military contracts, seeking to weaken the regime and remove foreign influence.
A border dispute between Iraq and Iran was resolved with the signing of the Algiers Accord on March 6, 1975.
However the economic improvements tended to only benefit a very small group and succeeded in disaffecting the vast majority of the population, culminating in widespread religious led protests throughout the late 1970s. There was widespread religious and political opposition to the Shah's rule and programs--especially [[SAVAK], the hated internal security and intelligence service. Martial law was declared in September 1978 for all major cities but the Shah recognized the erosion of his power-base and fled Iran on January 16, 1979.

Islamic Revolution

After many months of popular protests against the rule of the Shah, Mohammad Reza Pahlavi was forced to flee the nation on January 16, 1979. After a period of internal competition over the future of Iran, the contest was eventually won by the alliance led by the Ayatollah Khomeini who supported making Iran a theocratic state. On February 1, 1979, Khomeini returned from France (after 15 years in exile in France, Turkey, and Iraq) overthrowing the shah's government on February 11 and becoming Iran's Supreme Leader.
The new government was extremely conservative. It nationalized industry and restored Islamic traditions in culture and law. Western influencees were banned and the existing pro-West elite was quick to join the shah in exile. There were clashes between rival religious factions and brutal repression quickly became commonplace.