Smith became Deputy Prime Minister following the Rhodesian Front's December 1962 election victory, and stepped up to the premiership after Field resigned in April 1964. With the UK government refusing to grant independence while Rhodesia did not devise a set timetable for the introduction of majority rule, talks with the UK Prime Minister Harold Wilson repeatedly broke down, leading Smith and his Cabinet to declare independence on 11 November 1965. His government endured in the face of United Nations economic sanctions with the assistance of South Africa and, until 1974, Portugal. Talks with the UK in 1966, 1968 and 1971 came to nothing. Smith declared Rhodesia a republic in 1970 and led the RF to three more decisive election victories over the next seven years. After the Bush War began in earnest in 1972, he negotiated with the non-militant nationalist leader Bishop Abel Muzorewa and the rival guerrilla movements headed by Joshua Nkomo and Robert Mugabe.