Fifty-two United States diplomats and citizens were held hostage after a group of militarized Iranian college students belonging to the Muslim Student Followers of the Imam's Line, who supported the Iranian Revolution, took over the U.S. Embassy in Tehran and seized hostages. A diplomatic standoff ensued. The hostages were held for 444 days from November 4, 1979, to January 20, 1981.
Western media described the crisis as an "entanglement" of "vengeance and mutual incomprehension." U.S. President Jimmy Carter called the hostage-taking an act of "blackmail" and the hostages "victims of terrorism and anarchy". In Iran it was widely seen as an act against the U.S. and its influence in Iran, including its perceived attempts to undermine the Iranian Revolution and its longstanding support of the shah of Iran, Mohammad Reza Pahlavi, who was overthrown in 1979.
After Shah Pahlavi was overthrown, he was admitted to the U.S. for cancer treatment. Iran demanded his return in order to stand trial for crimes that he was accused of committing during his reign. Specifically, he was accused of committing crimes against Iranian citizens with the help of his secret police.