The Iranian Revolution in 1979 led to the overthrow of the Shah. The government was now an Islamic republic under the rule of Ayatollah Khomeini.
On January 16, 1979, the Shah fled Iran in temporary exile to the United States for medical reasons, although Iran believed he was given political asylum. Khomeini became supreme leader by December 1979 and installed an anti-Western theocracy.
Iranian Revolution, 1979, New York Times
U.S Embassy in Terhan, November 4, 1979, Wikepedia
“Today's move by a group of our compatriots is a natural reaction to the U.S. Government's indifference to the hurt feelings of the Iranian people about the presence of the deposed Shah, who is in the United States under the pretext of illness."
“If the U.S. authorities respected the feelings of the Iranian people and understood the depth of the Iranian revolution, they should have at least not allowed the deposed Shah into the country and should have returned his property.”
~The Iranian Foreign Ministry; Pars News Agency; November 5, 1979