In 1948, south african leaders adopted a policy of legal segregation of the white and black races

The correct answer is Apartheid. It lasted in South Africa for long and was mostly about separating the white population that was predominantly of Dutch origin from the African population that was made out of locals. The fight of Nelson Mandela against it became famous worldwide.

Sorry sir you did not give us the graph i typically but i'm very confused my conclusion is you're missing valuable information in the question