The South Africans doing more to prop up Rhodesia and Portugal instead of recognizing them as lost causes in the 1970's would be one start, but I'm not really sure how it would happen. Maybe a more stable domestic situation in South Africa?
I think a different Congo is probably the best catalyst, whether it's a more protracted Simba rebellion (though the U.S. would probably have been drawn into a Vietnam-like situation if the Simbas had been less of a joke) or maybe Lumumba remaining in power and having to fight a South African/Rhodesian-backed Katangan government? I've looked through the Congo Crisis for PODs in the past and the problem you have there is that the U.S. is going to weigh in against any leftist government. Maybe get rid of Mobutu to prevent strong central government from forming and keep the pot bubbling? Something like the initial Congo Crisis in 1970 instead of 1960 is going to see a very different Africa, with Rhodesia as a pariah state instead of a solid part of the Western bloc and a United States that's much more shy about getting involved in jungle insurgencies.
I don't know how you could drag West African powers into a war that starts in the Congo, though.