Tanganyika was a sovereign state, comprising the mainland part of present-day Tanzania, that existed from 1961 until 1964. It first gained independence from the United Kingdom on 9 December 1961 as a Commonwealth realm headed by Queen Elizabeth II before becoming a republic within the Commonwealth of Nations a year later. After signing the Articles of Union on 22 April 1964 and passing an Act of Union on 25 April, Tanganyika officially joined with the People's Republic of Zanzibar to form the United Republic of Tanganyika and Zanzibar on Union Day, 26 April 1964. The new state changed its name to the United Republic of Tanzania within a year.

Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to the south; Zambia to the southwest; and Rwanda, Burundi, and the Democratic Republic of the Congo to the west. Mount Kilimanjaro, Africa's highest mountain, is in northeastern Tanzania. According to the 2022 national census, Tanzania has a population of nearly 62 million, making it the most populous country located entirely south of the equator.