Question

"what was the system of legal segregation of people by race, ethnicity, and ancestry used in south africa until the early 1990s"

Answer 1

The system of legal segregation of people used in South Africa was known as apartheid.  It was instituted during era of European imperialism, when South Africa was colonized by the Dutch and the British.  It was similar in many ways to segregation in the United States following the Civil War.