Apartheid was a discriminatory policy in effect in South Africa for many years. It classified non-white people officially as less than equal under the law. Non whites couldn't work at jobs they chose, they couldn't choose where they lived. Non whites went to inferior schools and when they sick they went to inferior non white hospitals. Black South Africans were not even citizens of the country. Officially they were citizens of some Bantustan or other.
Those who supported apartheid in South Africa and in the United States appealed to the Bible. The Bible mythology states that Cane, son of Adam and Eve murdered his brother Able. Afterwards God marked Kane and his descendants. His descendants were unjustly cursed for their ancestor’s sin. White Christians looking for an excuse to treat black people as inferior claim that this mark was a dark skin. There is no reason to believe that, the Bible says nothing about what the mark was. Another piece of mythology is that after the Great flood Noah got drunk and got naked. His son Ham saw Noah naked and his descendants were [[cursed and marked. Again white Racists interpret the mark the way they like. If you really feel you must believe Bronze Age Mythology it's just as reasonable to imagine that the mark is a white skin.
White supremacista also argued from long-standing tradition (see article on "Proof") to support their contention that non-white people were of lower intelligence and generally prone to a number of bad habits. Both countries also banned marriage between the races, claiming that such a union was against God's will. If you have noticed any similarity to the current conservative stance towards homosexuality and gay marriage, you must be a conspiracy theorist or a liberal.