<P> Shi'a clergy (or Ulema,) have had a significant influence in Iran . The clergy first showed themselves to be a powerful political force in opposition to Iran's monarch with the 1891 Tobacco Protest boycott that effectively destroyed an unpopular concession granted by the shah giving a British company a monopoly over buying and selling Tobacco in Iran . To some the incident demonstrated that the Shia ulama were "Iran's first line of defense" against colonialism . </P> <P> The dynasty that the revolution overthrew--the Pahlavi dynasty--was known for its autocracy, its focus on modernization and Westernization and for its disregard for religious and democratic measures in Iran's constitution . </P> <P> The founder of the dynasty, army general Reza Pahlavi, replaced Islamic laws with western ones, and forbade traditional Islamic clothing, separation of the sexes and veiling of women (hijab). Women who resisted his ban on public hijab had their chadors forcibly removed and torn . In 1935 a rebellion by pious Shi'a at the shrine of Imam Reza in Mashhad was crushed on his orders with dozens killed and hundreds injured, rupturing relations between the Shah and pious Shia in Iran . </P> <P> Reza Shah was deposed in 1941 by an invasion of allied British and Soviet troops who believed him to be sympathetic with the allies' enemy Nazi Germany . His son, Mohammad Reza Pahlavi was installed by the allies as monarch . Prince Pahlavi (later crowned shah) reigned until the 1979 revolution with one brief interruption . In 1953 he fled the country after a power - struggle with his Prime Minister Mohammad Mossadegh . Mossadegh is remembered in Iran for having been voted into power through a democratic election, nationalizing Iran's British - owned oil fields, and being deposed in a military coup d'état organized by an American CIA operative and aided by the British MI6 . Thus foreign powers were involved in both the installation and restoration of Shah Mohammad Reza Pahlavi . </P>

Why did the islamic revolution occur in iran