The Unilateral Declaration of Independence (UDI) was a statement adopted by the Cabinet of Rhodesia on 11 November 1965, announcing that Southern Rhodesia or simply Rhodesia, a British territory in southern Africa that had governed itself since 1923, now regarded itself as an independent sovereign state. The culmination of a protracted dispute between the British and Rhodesian governments regarding the terms under which the latter could become fully independent, it was the first unilateral break from the United Kingdom by one of its colonies since the United States Declaration of Independence in 1776. The UK, the Commonwealth and the United Nations all deemed Rhodesia's UDI illegal, and economic sanctions, the first in the UN's history, were imposed on the breakaway colony. Amid near-complete international isolation, Rhodesia continued as an unrecognised state with the assistance of South Africa and (until 1974) Portugal.

The Rhodesian government, which mostly comprised members of the country's white minority of about 5%, was indignant when, amid the UK colonial government's Wind of Change policies of decolonisation, less developed African colonies to the north without comparable experience of self-rule quickly advanced to independence during the early 1960s while Rhodesia was refused sovereignty under the newly ascendant principle of "no independence before majority rule" ("NIBMAR"). Most white Rhodesians felt that they were due independence following four decades of self-government, and that the British government was betraying them by withholding it.

A stalemate developed between the British and Rhodesian prime ministers, Harold Wilson and Ian Smith respectively, between 1964 and 1965. The dispute largely surrounded the British condition that the terms for independence had to be acceptable "to the people of the country as a whole"; Smith contended that this was met, while the UK and African Nationalist Rhodesian leaders held that it was not. After Wilson proposed in late October 1965 that the UK might safeguard future black representation in the Rhodesian parliament by withdrawing some of the colonial government's devolved powers, then presented terms for an investigatory Royal Commission that the Rhodesians found unacceptable, Smith and his Cabinet declared independence. Calling this treasonous, the British colonial governor, Sir Humphrey Gibbs, formally dismissed Smith and his government, but they ignored him and appointed an "Officer Administering the Government" to take his place.

While no country recognised the UDI, the Rhodesian High Court deemed the post-UDI government legal and de jure in 1968. The Smith administration initially professed continued loyalty to Queen Elizabeth II, but abandoned this in 1970 when it declared a republic in an unsuccessful attempt to win foreign recognition. The Rhodesian Bush War, a guerrilla conflict between the government and two rival communist-backed black Rhodesian groups, began in earnest two years later, and after several attempts to end the war Smith concluded the Internal Settlement with non-militant nationalists in 1978. Under these terms the country was reconstituted under black rule as Zimbabwe Rhodesia in June 1979, but this new order was rejected by the guerrillas and the international community. The Bush War continued until Zimbabwe Rhodesia revoked its UDI as part of the Lancaster House Agreement in December 1979. Following a brief period of direct British rule, the country was granted internationally recognised independence under the name Zimbabwe in 1980.

Northern Rhodesia was a British protectorate in south central Africa, now the independent country of Zambia. It was formed in 1911 by amalgamating the two earlier protectorates of Barotziland-North-Western Rhodesia and North-Eastern Rhodesia. It was initially administered, as were the two earlier protectorates, by the British South Africa Company (BSAC), a chartered company, on behalf of the British Government. From 1924, it was administered by the British Government as a protectorate, under similar conditions to other British-administered protectorates, and the special provisions required when it was administered by BSAC were terminated.Although under the BSAC charter it had features of a charter colony, the BSAC's treaties with local rulers, and British legislation, gave it the status of a protectorate. The territory attracted a relatively small number of European settlers, but from the time they first secured political representation, they agitated for white minority rule, either as a separate entity or associated with Southern Rhodesia and possibly Nyasaland. The mineral wealth of Northern Rhodesia made full amalgamation attractive to Southern Rhodesian politicians, but the British Government preferred a looser association to include Nyasaland. This was intended to protect Africans in Northern Rhodesia and Nyasaland from discriminatory Southern Rhodesian laws. The Federation of Rhodesia and Nyasaland formed in 1953 was intensely unpopular among the vast African majority and its formation hastened calls for majority rule. As a result of this pressure, the country became independent in 1964 as Zambia.The geographical, as opposed to political, term "Rhodesia" referred to a region generally comprising the areas that are today Zambia and Zimbabwe. From 1964, it only referred to the former Southern Rhodesia.