Nelson Mandela was a good leader because he sought reconciliation with his political enemies rather than retaliation against them. This forgiving approach helped his country, South Africa, to heal from the wound of apartheid.
Under the racist apartheid regime, only white citizens of South Africa were permitted to participate in government and hold the best positions in all of the country's institutions. Black people, who were the majority of the population, were consigned to menial jobs and had little power even in the Bantustans created by the white government as semi-autonomous "homelands" for black South Africans.
Mandela himself was subject to even greater oppression, spending 27 years in prison for his belief that all South Africans should participate in society; however, when released, he did not punish his former captors. As president, he championed a policy of reconciliation, serving in a government of national unity with former members of the apartheid regime and writing a constitution that guaranteed respect for all people in South Africa. He also set up the Truth and Reconciliation Commission, where victims of apartheid had the opportunity to share their experiences. The commission also allowed perpetrators to receive amnesty, but only if they admitted their crimes. Finally, he began working to guarantee economic justice for the black South Africans who had been left out for so long. Mandela's approach helped his country avoid the flight of capital seen in countries like Zimbabwe, where Robert Mugabe's vengeful ruling style caused economic destruction on a huge scale. As of March 2014, in fact, South Africa is the richest country in Africa.