Taken from PBS here
According to the Federation of American Scientists,The United States ‘ and Israeli intelligence officers work with Iran to set up SAVAK, an Iranian intelligence organization later blamed for the torture and execution of thousands of political prisoners and violent suppression of dissent.
The shah implements “The White Revolution,” an aggressive campaign of social and economic Westernization that is met with intense popular opposition. Popular nationalist Ayatollah Khomeini is arrested in one of many crackdowns on the shah’s opponents. By the late 1960s the shah relies regularly on SAVAK to quell dissidence.
In one of a series of reforms that alienate his people, the shah replaces the Islamic calendar with an “imperial” calendar, beginning with the founding of the Persian Empire. Many of the shah’s growing number of critics see this as anti-Islamic.
Iranians resort to rioting, mass demonstrations and strikes to protest the shah’s authoritarian rule. In response, he enforces martial law.
The shah flees Iran amid intensifying unrest.
Islamic nationalist Ayatollah Khomeini returns from France, where he was exiled for his opposition to the shah’s regime. He encourages the brewing revolution.
Under Ayatollah Khomeini’s guidance, Iran declares itself a theocratic republic guided by Islamic principles, and a referendum is held to name it the Islamic Republic of Iran.
Islamic students storm the U.S. Embassy in Tehran, taking hostage 52 American employees and demand that the shah return from receiving medical treatment in the United States to face trial in Iran. Ayatollah Khomeini applauds their actions. The hostage situation ignites a crisis between the United States and Iran.
Iran and the United States sever diplomatic ties over the hostage crisis, and the U.S. Embassy becomes a training ground for the Revolutionary Guards Corps.
The shah dies in exile in Egypt