Vance pushed for détente with the Soviet Union, and clashed frequently with the hawkish Brzezinski. Vance tried to advance arms limitations by working on the SALT II agreement with the Soviet Union, which he saw as the central diplomatic issue of the time, but Brzezinski lobbied for a tougher, more assertive policy vis-à-vis the Soviets. He argued for strong condemnation of Soviet activity in Africa and in the Third World as well as successfully lobbying for normalized relations with the People's Republic of China in 1978. As Brzezinski took control of the negotiations with Beijing, Vance was marginalized and his influence began to wane. When revolution erupted in Iran in late 1978, the two were divided on how to support the United States' ally the Shah of Iran. Vance argued in favor of reforms while Brzezinski urged him to crack down – the 'iron fist' approach. Unable to receive a direct course of action from Carter, the mixed messages that the shah received from Vance and Brzezinski contributed to his confusion and indecision as he fled Iran in January 1979 and his regime collapsed. After Vance resigned in 1980, Carter appointed Edmund Muskie, a well-respected senator with whom Carter had developed friendly relations, to serve as Secretary of State.