The 1979 Revolution, later known as the ''Islamic Revolution'', began in January 1978 with the first major demonstrations against the Shah. After a year of strikes and demonstrations paralyzing the country and its economy, Mohammad Reza Pahlavi fled to the United States, and Ruhollah Khomeini returned from exile to Tehran in February 1979, forming a new government. After holding a referendum, Iran officially became an Islamic republic in April 1979. A second referendum in December 1979 approved a theocratic constitution.