Archeological findings have placed 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 B.C. saw a fairly sophisticated agricultural society and proto-urban population centers. Many dynasties have ruled Iran, the first of which was the Achaemenid (559-330 B.C.), a dynasty founded by Cyrus the Great. After the Hellenistic period (300-250 B.C.) came the Parthian (250 B.C.-226 A.D.) and the Sassanian (226-651) dynasties.

The seventh century Arab-Muslim conquest of Iran was followed by conquests by the Seljuk Turks, the Mongols, and Tamerlane. Iran underwent a revival under the Safavid dynasty (1502-1736), the most prominent figure of which was Shah Abbas. The conqueror Nadir Shah and his successors were followed by the Zand dynasty, founded by Karim Kahn, and later the Qajar (1795-1925) and the Pahlavi dynasties (1925-1979).

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, and the discovery of oil in 1908. In 1921, Reza Khan, an Iranian officer of the Persian Cossack Brigade, seized control of the government. In 1925, he made himself Shah, ruling as Reza Shah Pahlavi for almost 16 years and installing the new Pahlavi dynasty.

Under his reign, Iran began to modernize and to secularize politics, and the central government reasserted its authority over the tribes and provinces. In September 1941, following the Allies' (United Kingdom-Soviet Union) occupation of western Iran, Reza Shah was forced to abdicate. His son, Mohammad Reza Pahlavi, became Shah and ruled until 1979.

During World War II, Iran was a vital link in the Allied supply line for lend-lease supplies to the Soviet Union. After the war, 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. These were ended in 1946. The Azerbaijan revolt crumbled after U.S. and UN pressure forced a Soviet withdrawal and Iranian forces suppressed the Kurdish revolt.

In 1951, Premier Mohammed Mossadeq, a militant nationalist, forced the parliament to nationalize the British-owned oil industry. Mossadeq was opposed by the Shah and was removed, but he quickly returned to power. The Shah fled Iran but returned when supporters staged a coup against Mossadeq in August 1953. Mossadeq was then arrested by pro-Shah army forces. 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.

In 1978, domestic turmoil swept the country as a result of religious and political opposition to the Shah's rule and programs--especially SAVAK, the hated internal security and intelligence service. In January 1979, the Shah left Iran; he died abroad several years after.

On February 1, 1979, exiled religious leader Ayatollah Ruhollah Khomeini returned from France to direct a revolution resulting in a new, theocratic republic guided by Islamic principles. Back in Iran after 15 years in exile in Turkey, Iraq, and France, he became Iran's national religious leader. Following Khomeini's death on June 3, 1989, the Assembly of Experts--an elected body of senior clerics--chose the outgoing president of the republic, Ali Khamenei, to be his successor as national religious leader in what proved to be a smooth transition.

In August 1989, Ali Akbar Hashemi-Rafsanjani, the speaker of the Majles, was elected President by an overwhelming majority. He was re-elected June 1993, with a more modest majority; some Western observers attributed the reduced voter turnout to disenchantment with the deteriorating economy. (Ali) Mohammad Khatami-Ardakani, elected President in August 1997 with an overwhelming majority, was re-elected again with a majority in June 2001. In February 2004 flawed elections were held for the 7 ^th Majles in which many reformists were prohibited from contesting their seats. The managed result was that a much more conservative Majles took its seats in May 2004.

Presidential elections took place on June 17, 2005, resulting in a two-candidate runoff between Mahmud Ahmadi-Nejad and Ali Akbar Hashemi Rafsanjani on June 24. On June 25, Mahmud Ahmadi-Nejad became President-elect; he took office in August 2005. The next presidential elections are scheduled for 2009.