Ayatollah Ruhollah Khomeini ruled Iran for 10 years after the revolution. Story Tools

(CNN) -- Tens of thousands of Iranians have been commemorating the 25th anniversary of the Islamic revolution. Here is a timeline of events that shaped Iran in the 20th century:

1920s: Army officer Reza Khan leads a coup that topples government. In 1925, he declares himself shah, or undisputed leader.

1935: Formerly known as Persia, "Iran" adopted as official name.

1940s: During World War II, Reza Khan, now Reza Shah Pahlavi, is forced by Britain and Russia to abdicate his throne in favor of his son, Mohammad Reza Shah Pahlavi, because the elder Pahlavi is seen as too pro-German.

1950s: Mohammad Reza Shah Pahlavi is forced to flee, as Nationalist premier Mohammed Mossadegh comes to power with plans to nationalize Iran's lucrative oil industry. In 1953, the shah, with Western backing, overthrows Mossadegh and returns to power.

1960s/1970s: Ayatollah Ruhollah Khomeini exiled in early 1960s. The Shah embarks on a campaign to modernize and Westernize his country.

1979: January: Shah flees from increased unrest led by Shiite Muslims. February 1: Khomeini arrives from exile. February 11: Shah's regime falls. April 1: Khomeini declares an Islamic Republic; November 4: Islamic militants take 52 Americans hostage inside the U.S. embassy in Tehran.

1980: The shah dies in exile.

1980-1988: War with Iraq.

1981: January 20: Hostages released

July 1988: The U.S. Navy mistakenly shoots down an Iranian passenger jet in the Persian Gulf, killing 290 people aboard.

1989: February: Khomeini calls on Muslims to kill author Salman Rushdie for insulting the religion. June: Khomeini dies and is succeeded by Ayatollah Ali Khamenei.

1997: Moderate cleric Mohammad Khatami is overwhelmingly elected president, besting hard-line candidates backed by the conservative Shiite clergy. Khatami calls for a "thoughtful dialogue with the American people."