It was the 1970's and there was Soviet, South African, U.S. and Cuban interest in Angola. There was a group called the Movement For The Liberation Of Angola (MPLA)-good guys. In the beginning Castro sent advisers to help the MPLA. Russia, Cuba's buddy wasn't totally enthused about committing money, troops and arms to the cause. The U.S.-and these were the days of Kissinger were interested in a certain oil rich area in the region. Kissinger claimed that the Russkies were heavily into the fight. (He had to spin it this way to get support.) The South African's then launched a secret invasion into the region in hopes of taking it over. Castro then said 'hell no' and eventually sent in 30,000 troops on his own dime, as the Russian said 'dude you're on your own'. The Cuban army defeated the South Africans putting down the secret invasion. Even after the defeat we (CIA) continued funding and supplied arms to a different rebel faction-bad guys. It didn't work. Neither Kissinger, Washington or the lovely U.S. press ever credited Castro with the victory. Or told the true version of the event for that matter. Years later Nelson Mandela thanked Cuba profusely for the effort and even that was somewhat buried in the back pages of a handful of newspapers.
For a far better account of the whole ordeal read:
Conflicting Missions-Havana, Washington and Africa By Piero Gleijeses.
This cat is a professor of American foreign policy at the School of Advanced International Studies at Johns Hopkins University. The book was published in Feb. 2003.