Apartheid contained enmity between black tribes by keeping them separated
https://www.unz.com/ghood/sights-and-sounds-south-africa/
Diverse societies fail. South Africa was waiting to riot and loot; all it needed was a spark. That spark: inter-tribal hatred within the black population.
People think of South African diversity as black/white, but the main diversity is between black tribes. Apartheid was as much about keeping the black tribes separated as it was keeping whites and blacks separated.