Throughout the 1970s, the Ayatollah Khomeni, the leading Shi'ite cleric in Iran, had pushed for the removal of Reza Pahlavi, the autocratic Shah of Iran who enjoyed the backing of the United States government. In 1979, thousands of students took to the streets of Tehran, launching a revolution that drove the Shah from power. Two weeks after the Shah abdicated in February, the Ayatollah returned to Teheran to assume control of the newly organized Islamic Republic of Iran. The Ayatollah's followers imprisoned and executed many of the Shah's supporters, as well as secularists who were less than enthusiastic about the strict Islamic regime that was coming to power. Some of the Ayatollah's followers seized control of the American embassy in Tehran, holding around fifty embassy employees hostage and sparking an international crisis that finally ended with the release of the hostages early in 1981. The Ayatollah's rise to power also led to a major, destructive war with neighboring Iraq that only ended in 1989.