Kingdom deemed the Rhodesian declaration an act of rebellion but did not re-establish control by force. The British government petitioned the United Nations for sanctions against Rhodesia pending unsuccessful talks with Smith's administration in 1966 and 1968. In December 1966, the organisation complied, imposing the first mandatory trade embargo on an autonomous state. These sanctions were expanded again in 1968. A civil war ensued when Joshua Nkomo's Zimbabwe African People's Union (ZAPU) and Robert Mugabe's Zimbabwe African National Union (ZANU), supported actively by communist powers and neighbouring African nations, initiated guerrilla operations against Rhodesia's predominantly white government. ZAPU was supported by the Soviet Union, the Warsaw Pact and associated nations such as Cuba, and adopted a Marxist–Leninist ideology; ZANU meanwhile aligned itself with Maoism and the bloc headed by the People's Republic of China. Smith declared Rhodesia a republic in 1970, following the results of a referendum the previous year, but this went unrecognised internationally. Meanwhile, Rhodesia's internal conflict intensified, eventually forcing him to open negotiations with the militant communists. In March 1978, Smith reached an accord with three African leaders, led by Bishop Abel Muzorewa, who offered to leave the white population comfortably entrenched in exchange for the establishment of a biracial democracy. As a result of the Internal Settlement, elections were held in April 1979, concluding with the United African National Council (UANC) carrying a majority of parliamentary seats. On 1 June 1979, Muzorewa, the UANC head, became prime minister and the country's name was changed to Zimbabwe Rhodesia. The Internal Settlement left control of the Rhodesian Security Forces, civil service, judiciary, and a third of parliament seats to whites. On 12 June, the United States Senate voted to lift economic pressure on the former Rhodesia. Following the fifth Commonwealth Heads of Government Meeting, held in Lusaka, Zambia, from 1 to 7 August in 1979, the British government invited Muzorewa, Mugabe, and Nkomo to participate in a constitutional conference at Lancaster House. The purpose of the conference was to discuss and reach an agreement on the terms of an independence constitution, and provide for elections supervised under British authority allowing Zimbabwe Rhodesia to proceed to legal independence. With Lord Carrington, Secretary of State for Foreign and Commonwealth Affairs of the United Kingdom, in the chair, these discussions were mounted from 10 September to 15 December in 1979, producing a total of 47 plenary sessions. On 21 December 1979,