“As I walked out the door toward the gate that would lead to my freedom, I knew if I didn't leave my bitterness and hatred behind, I'd still be in prison.” Thus when apartheid was renounced, Mandela worked hard to avoid a bloodbath and political things that some other African nations undertook to their detriment. Instead he worked hard for a South Africa for all its people in his one term as president where he founded the Truth and Reconciliation Commission to deal with past injustices made by all sides.
Though it took more than sanctions and calls for divestment of U.S. company stock from university and state balance sheets (most notably California), the sanctions and divestment did put pressure on South Africa to change its ways.* And the U.S. congress overrode a veto by President Reagan to pass the Comprehensive Anti-Apartheid Act of 1986.
Nelson Mandela shared a Nobel Peace prize with the leader he superseded Frederik Willem de Klerk in 1993 "for their work for the peaceful termination of the apartheid regime, and for laying the foundations for a new democratic South Africa".***