You have it wrong. Far from wanting a a slave population of blacks, etc the South Africans bankrupted themselves building up adjacent countries (homelands) with superb infrastructure, airports, universities, harbours, etc in the forlorn hope that they could persuade the black population to move there. Unfortunately, even at the height of Grand Apartheid, blacks from every part of Africa were fighting to gain entrance to South Africa, just as they are now camping at Calais.