Map of the Angolan Civil War during January - March 1976.
Following the FNLA defeat at Quifangondo and the announcement of South Africa's withdrawal, the MPLA, backed by Cuban forces, launched multiple offensives to retake lost ground and eventually take control of all of Angola. Being spread too thin and with foreign support now gone, the FNLA and UNITA were quickly overrun by the MPLA advance. By the end of March 1976, the MPLA had effectively taken control of the whole country. While this practically destroyed the FNLA as a fighting force, UNITA switched tactics and launched a guerrilla war.
Sources used:

Edward George's "The Cuban Intervention in Angola 1965-1991 From Che Guevara to Cuito Cuanavale"
Adrien Fontanellaz's and Tom Cooper's "War of Intervention in Angola: Volume 1 - Angolan and Cuban Forces at War, 1975-1976"
Stephen Weigert's "Angola: A Modern Military History, 1961-2002"
Own work
Rr016