In 1960 an area which declared itself as the State, or Republic, of Katanga seceded from which country?

Question

Which country became a self-governing state within the British Empire in 1959, declared independence from Britain, joining the Federation of Malaysia in 1963, and left the federation on 9 August 1965?

Answer 1

Republic of Congo-Léopoldville
The Republic was conquered in 1963 by a combination of western and Congolese interests including UN forces. Congo-Léopoldville is currently known as the Democratic Republic of the Congo. Despite ongoing armed activity where it became a province and seceded again Katanga was split in 2015 into three Congolese provinces.