The Uganda–Tanzania War, known in Tanzania as the Kagera War (Swahili: Vita vya Kagera) and in Uganda as the 1979 Liberation War, was fought between Uganda and Tanzania from October 1978 until June 1979 and led to the overthrow of Ugandan President Idi Amin. The war was preceded by a deterioration of relations between Uganda and Tanzania following Amin's 1971 overthrow of President Milton Obote, who was close to the President of Tanzania, Julius Nyerere. Over the following years, Amin's regime was destabilised by violent purges, economic problems, and dissatisfaction in the Uganda Army.
The circumstances surrounding the outbreak of the war are not clear, and differing accounts of the events exist. In October 1978, Ugandan forces began making incursions into Tanzania. Later that month, the Uganda Army launched an invasion, looting property and killing civilians. Ugandan official media declared the annexation of the Kagera Salient. On 2 November, Nyerere declared war on Uganda and mobilised the Tanzania People's Defence Force (TPDF) to retake the salient. Nyerere also mobilised Ugandan rebels loyal to Obote and Yoweri Museveni to weaken Amin's regime. After Amin failed to renounce his claims to Kagera and the Organisation of African Unity (OAU) failed to condemn the Ugandan invasion, the TPDF occupied the towns of Masaka and Mbarara in southern Uganda.