In 1970, Iran signed the Non-Proliferation Treaty. The participation of the US and Western European governments in Iran’s nuclear programme continued until the 1979 Iranian Revolution, which toppled the regime of the last Shah of Iran, Mohammad Reza Pahlavi. Following the 1979 Revolution, most of the international community’s nuclear cooperation with Iran was withdrawn, but in the 1990s, Russia formed a joint research organization with Iran, providing the country with Russian nuclear experts and technical information.