Early History: The first Iranian state was the Achaemenian Empire, which was established by Cyrus the Great in 546 B.C. Alexander the Great conquered the empire in 330 B.C. The Greek rule was followed by the Parthians, who ruled from 247 B.C. until A.D. 224, and the Sassanians, who ruled from A.D. 224 until the Arabs conquered Iran in A.D. 651. The Arabs brought with them Islam, which eventually became the predominant religion. In the centuries that followed, Iran was ruled by a succession of Arab, Iranian, and Turkic dynasties. In the thirteenth century, the Mongol leader Genghis Khan invaded the disunified territory of Iran, and Mongol dynasties subsequently ruled Iran for nearly two centuries. In 1501 the Iranian Safavis created a strong centralized empire under Ismael I and also established Shia Islam as the official religion. In the eighteenth century, Iran was weakened by civil wars, new dynasties came to rule, and a new regional rival, Russia, arose.

The Qajars and Pahlavis: In 1794 the Qajar family established a dynasty that would rule Iran until 1925. In the nineteenth century, Iran, under the Qajars, lost much of its territory in the Caucasus and Central Asia to Russia. During this period, influence in Iran was divided between Russia and Britain, Russia’s chief Western rival in the region. Both powers interfered in local politics and forced Iran to make trade concessions. A popular desire for accountable government and resentment of intrusion by foreign interests led to the Constitutional Revolution of 1905–6 and the formation of a parliament. In 1909 the Anglo-Persian Oil Company was formed and assumed control of Iran’s newly discovered oil deposits.

In 1921 army officer Reza Khan provided military support for a coup against the government; he was named minister of defense, then prime minister. Following parliament’s deposition of the Qajar dynasty in 1925, he became shah of Iran, adopting the surname of Pahlavi. As Reza Shah Pahlavi, he restored order and sought to modernize the economy and society and to forge cultural links abroad. However, in World War II his failure to cooperate with the Allied powers caused Britain and the Soviet Union to invade Iran and force him to abdicate in favor of his son, Mohammed Reza Shah Pahlavi. In 1951 Mohammad Mossadeq, a deputy in the parliament, rode strong Iranian sentiment for nationalization of the oil industry to a position as prime minister. However, in 1953 Britain and the United States, which opposed the principle of oil nationalization at the time, forced the nationalist Mossadeq from power.

In the 1960s, Iran recovered from the economic disruption of the oil nationalization period, but the authoritarian rule of the shah provoked political discontent. It was during this period that Ayatollah Ruhollah Khomeini developed a following as an antigovernment leader and was sent into exile (1964), first to Turkey and subsequently to Iraq. Between 1965 and 1977, Iran enjoyed improved prosperity, expanded regional influence, and relative stability. However, there was no liberalization of the political system, and repression coupled with resentment of an increased Western presence fueled a series of antigovernment protests in 1977 and early 1978 that developed into a nationwide revolutionary movement. From his exile base in Iraq, Khomeini emerged as the leader of an increasingly strong opposition movement, which organized nationwide strikes and effectively paralyzed the economy by late 1978. The military, experiencing mass desertions and the refusal of junior officers to act against strikers and demonstrations, was unable to protect the regime, and the shah decided to leave the country, ostensibly for medical treatment. After the shah’s departure, his government was unable to stem what had become a revolutionary tide. Khomeini returned from exile on February 1, 1979, refused to recognize the authority of the shah’s prime minister, and appointed a provisional government. When the military announced its neutrality in the power struggle between the two governments, the monarchy effectively ended.

The Islamic Republic of Iran: Following a national plebiscite, an Islamic republic was proclaimed officially on April 1, 1979. The provisional government was composed of a coalition of nationalist and religious leaders who had moderate views with respect to social and economic changes. They were opposed by young militants who advocated radical changes in both domestic and foreign policies. In particular, the latter group wanted to end all ties with the United States. In November 1979, students affiliated with the latter group occupied the U.S. Embassy in Tehran and held 53 U.S. diplomats hostage for the next 14 months. This incident led to the collapse of the provisional government and a decisive break in U.S.-Iranian relations. Between 1980 and 1988, serious differences between the moderate and militant factions of the revolutionary government were held in check by the need to maintain internal unity during an indecisive war with Iraq that resulted in more than 200,000 Iranian deaths.

In 1989 the death of Khomeini removed the one figure with authority to arbitrate between the two mutually antagonistic political factions of the postrevolutionary elite. Neither of the two factions constituted a homogeneous political group; rather, each comprised multiple ideological tendencies. In general, those whom the Western press labeled “reformers” advocated a liberal interpretation of the constitution and Islamic law but disagreed among themselves with respect to economic, political, and social policies. By contrast, those who came to be known as “conservatives” advocated the strict and literal interpretation of the constitution and Islamic law.

During the presidency of Ali Akbar Hashemi Rafsanjani (1989–97), reformers controlled a majority of seats in parliament until 1992 and supported Rafsanjani’s policies for economic reform and the normalization of relations with neighboring countries. The conservatives won a majority of seats in both the 1992 and 1996 parliamentary elections and subsequently used their position in the legislature to weaken or stop outright many reforms proposed by the Rafsanjani government. The administrations of Rafsanjani’s successor, Mohammad Khatami (in office 1997–2005), encountered the same resistance. Reformers won a majority of seats in the 2000 parliamentary elections and then enacted several notable pieces of reform legislation in the ensuing term. Having lost control of the parliament, conservatives tried to use their influence in the judiciary and bureaucracy to impede reforms they perceived as threatening their positions. Conservatives regained control of the parliament in the February 2004 elections.

Although Iran’s foreign relations had improved under Khatami, in the early 2000s earlier progress was eroded by Iran’s ostensible support of terrorist groups in the Middle East and conflict with the European Union and the United States over Iran’s nuclear program. Iran’s international position was jeopardized by the construction of nuclear processing plants to provide fuel for its nuclear energy generating facility at Bushehr, which was being built with significant technical input from Russia. In mid-2005 the surprise election of conservative Mahmoud Ahmadinejad as president led Iran to adopt more confrontational international positions, especially vis-à-vis limitations on its nuclear fuel processing program and its attitude toward Israel. Within Iran, moderate and conservative factions concurred in defending the nuclear program against international interference.