In 1975–1976, South Africa's apartheid regime took the momentous step of intervening in the Angolan civil war to counter the Marxist Popular Movement for the Liberation of Angola and its backers in Havana and Moscow. The failure of this intervention and the subsequent ignominious withdrawal had major repercussions for the evolution of the regime and the history of the Cold War in southern Africa. This article is the first comprehensive study of how and why Pretoria became involved. Drawing on a wide variety of primary sources from South African archives as well as interviews with key protagonists, the article shows that the South African Defence Force and Defence Minister P. W. Botha pushed vigorously and successfully for deeper engagement to cope with security threats perceived through the prism of the emerging doctrine of “total onslaught.” South Africa's intervention in Angola was first and foremost the product of strategic calculations derived from a sense of threat perception expressed and experienced in Cold War terms, but applied and developed in a localized southern African context.