Back on 11 November 1965, Ian Smith's white minority government in Rhodesia signed the Unilateral Declaration of Independence, UDI, as a response to the British government's attempt to push forwards with black majority rule. The move was condemned by Britain and the United Nations. The timing of the declaration was a reminder to the British government that white Rhodesians had sacrificed their lives for Britain in two world wars, and that the motherland should not turn her back on them now.
Britain, and then the UN imposed sanctions against Ian Smiths government, and the country struggled forward with help from South Africa (although they didn't officially recognize the declaration of independence) and Portugal (through Mozambique, until Samora Machel came to power).
Ian Smith had wanted Rhodesia to remain a Commonwealth country, but stymied by international condemnation he put the prospect of Rhodesia becoming a republic to a whites only referendum in 1969. On 2 March 1970 Rhodesia was declared a republic, although the international community did not recognize the move and continued with sanctions.
By 1978 Smith and his government were yielding to international pressure, and a British supervised election in 1980 brought Robert Mugabe to power.