In 549 BC Cyrus the Great united the Medes and Persians in the Persian Empire, conquered Babylonia in 538 BC, restored Jerusalem to the Jews. Alexander the Great conquered Persia in 333 BC, but Persians regained their independence in the next century under the Parthians, themselves succeeded by Sassanian Persians in 226 AD. Arabs brought Islam to Persia in the 7th century, replacing the indigenous Zoroastrian faith. After Persian political and cultural autonomy was reasserted in the 9th century, the arts and sciences flourished for several centuries.

Turks and Mongols ruled Persia in turn from the 11th century to 1502, when a native dynasty reasserted full independence. The British and Russian empires vied for influence in the 19th century, and Afghanistan was severed from Iran by Britain in 1857.

Reza Khan abdicated as shah, 1941, and was succeeded by his son, Mohammed Reza Pahlavi. Under his rule, Iran underwent economic and social change but political opposition was not tolerated.

Conservative Muslim protests led to 1978 violence. Martial law in 12 cities was declared Sept. 8. A military government was appointed Nov. 6 to deal with striking oil workers. Prime Min. Shahpur Bakhtiar was designated by the shah to head a regency council in his absence. The shah left Iran Jan. 16, 1979.

Exiled religious leader Ayatollah Ruhollah Khomeini named a provisional government council in preparation for his return to Iran, Jan. 31. Clashes between Khomeini’s supporters and government troops culminated in a rout of Iran’s elite Imperial Guard Feb. 11, leading to the fall of Bakhtiar’s government.

The Iranian revolution was marked by revolts among the ethnic minorities and by a continuing struggle between the clerical forces and westernized intellectuals and liberals. The Islamic Constitution established final authority to be vested in a Faghi, the Ayatollah Khomeini.

Iranian militants seized the U.S. embassy, Nov. 4, 1979, and took hostages including 62 Americans. Despite international condemnations and U.S. efforts, including an abortive Apr. 1980 rescue attempt, the crisis continued. The U.S. broke diplomatic relations with Iran, Apr. 7. The shah died in Egypt, July 27. The hostage drama finally ended Jan. 21, 1981, when an accord, involving the release of frozen Iranian assets, was reached.

A dispute over the Shatt al-Arab waterway that divides the two countries brought Iran and Iraq, Sept. 22, 1980, into open warfare. Iraqi planes attacked Iranian air fields including Tehran airport. Iranian planes bombed Iraqi bases. Iraqi troops occupied Iranian territory including the port city of Khorramshahr in October. Iranian troops recaptured the city and drove Iraqi troops back across the border, May 1982. Iraq, and later Iran, attacked several oil tankers in the Persian Gulf during 1984. Saudi Arabian war planes shot down 2 Iranian jets, June 5, which they felt were threatening Saudi shipping. In Aug. 1988, Iran agreed to accept a UN resolution calling for a cease-fire.

In Nov. 1986, senior U.S. officials secretly visited Iran and exchanged arms for Iran’s help in obtaining the release of U.S. hostages held by terrorists in Lebanon. The exchange sparked a major scandal in the Reagan administration.

A U.S. Navy warship shot down an Iranian commercial airliner, July 3, 1988, after mistaking it for an F-14 fighter jet; all 290 aboard the plane died.

A major earthquake struck northern Iran June 21, 1990, killing more than 45,000, injuring 100,000, and leaving 400,000 homeless. A U.S. offer of assistance was accepted by the Iranian government.