Faced with an army mutiny and violent demonstrations against his rule, Mohammad Reza Shah Pahlavi, the leader of Iran since 1941, is forced to flee the country. Fourteen days later, the Ayatollah Ruhollah Khomeini, the spiritual leader of the Islamic revolution, returned after 15 years of exile and took control of Iran.

In 1941, British and Soviet troops occupied Iran, and the first Pahlavi shah, who they regarded with suspicion, was forced to abdicate in favor of his son, Mohammad Reza. The new shah promised to act as a constitutional monarch but often meddled in the elected government’s affairs. After a Communist plot against him was thwarted in 1949, he took on even more powers. However, in the early 1950s, the shah was eclipsed by Mohammad Mosaddeq, a zealous Iranian nationalist who convinced the Parliament to nationalize Britain’s extensive oil interests in Iran. Mohammad Reza, who maintained close relations with Britain and the United States, opposed the decision. Nevertheless, he was forced in 1951 to appoint Mosaddeq premier, and two years of tension followed.

In August 1953, Mohammad Reza attempted to dismiss Mosaddeq, but the premier’s popular support was so great that the shah himself was forced out of Iran. A few days later, British and U.S. intelligence agents orchestrated a stunning coup d’etat against Mosaddeq, and the shah returned to take power as the sole leader of Iran. He repealed Mosaddeq’s legislation and became a close Cold War ally of the United States in the Middle East.

In 1963, the shah launched his “White Revolution,” a broad government program that included land reform, infrastructure development, voting rights for women, and the reduction of illiteracy. Although these programs were applauded by many in Iran, Islamic leaders were critical of what they saw as the westernization of Iran. Ruhollah Khomeini, a Shiite cleric, was particularly vocal in his criticism and called for the overthrow of the shah and the establishment of an Islamic state. In 1964, Khomeini was exiled and settled across the border in Iraq, where he sent radio messages to incite his supporters.

The shah saw himself foremost as a Persian king and in 1971 held an extravagant celebration of the 2,500th anniversary of the pre-Islamic Persian monarchy. In 1976, he formally replaced the Islamic calendar with a Persian calendar. Religious discontent grew, and the shah became more repressive, using his brutal secret police force to suppress opposition. This alienated students and intellectuals in Iran, and support for Khomeini grew. Discontent was also rampant in the poor and middle classes, who felt that the economic developments of the White Revolution had only benefited the ruling elite. In 1978, anti-shah demonstrations broke out in Iran’s major cities.

On September 8, 1978, the shah’s security force fired on a large group of demonstrators, killing hundreds and wounding thousands. Two months later, thousands took to the streets of Tehran, rioting and destroying symbols of westernization, such as banks and liquor stores. Khomeini called for the shah’s immediate overthrow, and on December 11 a group of soldiers mutinied and attacked the shah’s security officers. With that, his regime collapsed and the shah fled.

The shah traveled to several countries before entering the United States in October 1979 for medical treatment of his cancer. In Tehran, Islamic militants responded on November 4 by storming the U.S. embassy and taking the staff hostage. With the approval of Khomeini, the militants demanded the return of the shah to Iran to stand trial for his crimes. The United States refused to negotiate, and 52 American hostages were held for 444 days. Mohammad Reza Shah Pahlavi died in Egypt in July 1980.

READ MORE: U.S.-Iran Tensions: From Political Coup to Hostage Crisis to Drone Strikes