During World War II, Britain and the USSR invaded Iran from August 25 to September 17, 1941, to stop an Axis supported coup and secure Iran's oil resources supply. The Allies of World War II forced the shah to abdicate in favor of his son, Mohammad Reza Pahlavi, who they hoped would be more supportive of them. In 1953, following the nationalization of the Anglo-Iranian Oil Company, democratically elected Prime Minister Mohammed Mossadegh attempted to convince the Shah to leave the country. The Shah refused, and formally dismissed the Prime Minister. Mossadegh also refused to leave, and when it became evident that he was going to fight, the Shah (as foreseen by the British/American "Operation Ajax") fled to Baghdad as a precautionary measure and on from there to Rome.
Massive protests broke out across the nation. Anti- and pro-monarchy protestors violently clashed in the streets, leaving almost 300 dead. The military intervened as the pro-Shah tank regiments stormed the capital and bombarded the prime minister's official residence. Mossadegh surrendered, and was arrested on August 19, 1953. Mossadegh was tried for treason, and sentenced to three years in prison.
The Shah was reinstated and power handed to Shah Mohammad Reza Pahlavi, whose rule became increasingly dictatorial in the following years, particularly the late 1970s. With strong support from the US and UK, the Shah further modernized Iranian industry, but simultaneously crushed opposition from the Shia clergy and from advocates of democracy.
In the 1970s, Ayatollah Ruhollah Khomeini gained much popularity among Iranians. Islamists, communists and liberals staged the Iranian Revolution of 1979, the Shah fled the country, after which Khomeini eventually succeeded in taking power and establishing an Islamic republic. The new system established conservative Islamic laws and unprecedented levels of direct clerical rule. Past governments have criticized the West and in particular the US for support of the Shah. Relations were severely strained in 1979, after Iranian students seized US embassy personnel. Subsequently, there were attempts to export the Islamic revolution, and support anti-Western militant groups such as Lebanese Hezbollah. From 1980-1988, Iran and neighbouring Iraq engaged in the destructive Iran-Iraq War.
The struggle between reformists and conservatives continues today through electoral politics, and was a central focus in the Iranian presidential election of 2005, which resulted in the election of Mahmoud Ahmadinejad. Since then, there has been an increase in tensions between Iran and the US, particularly with regard to Iran's nuclear program. Iran claims the right to research nuclear energy for peaceful purposes, under the Nuclear Non-Proliferation Treaty, which it has signed. It has been reported that the Bush Administration has not ruled out using nuclear weapons against Iran which, if it were to occur, would be the first hostile nuclear bombing since World War II. Other members of the UN Security Council, in particular Russia and China, oppose military action. Significantly, Iran was recently elected vice-chair on the UN Disarmament Commission. Recently, Iran announced it is researching the construction of a P2 centrifuge, which can be used to develop nuclear weapons.