4000 B.C. Ancient settlements develop in the Caspian region and on the Iranian plateau.
2000 B.C. Aryans arrive and split into the Medes and the Persians.
550 B.C. Cyrus the Great founds the Persian Empire.
200 A.D. After periods of Greek and Parthian rule, the Sassanids take power and rule until the Arab final victory in 641.
1502. The Safavid dynasty is established and continues to rule until 1736.
1904. The Qajar dynasty, founded by Fath Ali Shah, comes to an end.
1906-08. Iran's modern history begins when the Constitutional Movement achieves the declaration of a constitution and the establishment of a parliament in 1906 and when oil is discovered in 1908.
1919. The country is occupied by Russia and Great Britain during World War I; it signs a trade agreement with Great Britain in 1919, in which Britain formally re-affirms Iran's independence.
1921. After Iranian recognition of the USSR, the Soviet Union withdraws occupation forces from Iranian territory; Reza Khan, an army officer, establishes military rule and subsequently becomes shah in 1925 and founder of the new Pahlevi dynasty.
1941. Iran is occupied by British and Soviet forces at the start of World War II, prompting the shah to abdicate in favor of his son, Muhammad Reza Shah Pahlevi.
1943-46. Iran is formally guaranteed independence by the United States, Great Britain, and the Soviet Union in 1943; however, political instability delays the withdrawal of troops until 1946.
1951-53. The National Front Movement under Prime Minister Mossadeq nationalizes the oil business and forms the National Iranian Oil Company (NIOC); Mossadeq is subsequently ousted from power with the help of U.S. covert activity, and an international consortium operates Iran's oil facilities, with profits shared equally between Iran and the consortium.
1960-73. The shah's modernization program—named the "white revolution"—transforms the country and its economy, with a dramatic land reform, huge investments in infrastructure, and continued economic growth.
1973. The shah gives the NIOC full control over Iran's oil industry, placing the international consortium in an advisory capacity. Iran does not participate in the Arab oil embargo in September.
1979. After years of political repression and with a growing divide between rich and poor, popular protests oust the shah in the Islamic Revolution of 1979. Ayatollah Khomeini becomes the figurehead of the revolution and subsequently the Supreme Leader of the country until his death in 1989.
1980. On 22 September, Iraqi troops invade Iran, triggering a prolonged and devastating war that lasts until Khomeini accepts a UN-brokered cease-fire in July 1988.
1989. The Ayatollah Khomeini is succeeded by Iran's president, Ali Khamenei. Ali Akbar Rafsanjani becomes president and is re-elected in 1993. Iran begins to re-build its economy.
1997. Mohammed Khatami, a moderately liberal Muslim cleric, is elected president and becomes the figure-head for the country's reformist movement; economic reforms begun under Rafsanjani continue.