Rhodesia's 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, 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.