I encountered a similar question before. Here's my answer:
Apartheid was the system of legislation that separated white from non-white, and non-white from each other using their tribal lines.
This was to ensure that the political power the groups have will not be strong enough to overpower the National Party.
International attention was gained when Nelson Mandela, a resistance leader and founder of Umkhonto we Sizwe (“Spear of the Nation”), was imprisoned. Thus, international pressure began to stop apartheid system.
1973 - United Nations General Assembly had denounced apartheid
1976 - UN Security Council voted to impose a mandatory embargo on the sale of arms to South Africa
1985 - the United Kingdom and United States imposed economic sanctions on the country (Africa).
1989 - F.W. de Klerk, with the support of Nelson Mandela and his supporters, step up as President.
