After the 1948 victory of the National Party with its policy of apartheid, Nelson increasingly became more active in the resistance movement. Apartheid was a system of institutionalized racism that created segregation between the often poorer blacks and the more affluent colonialists.
Influenced by Ghandi, Nelson initially advocated peaceful protest through his membership in the ANC. But in 1961 he became leader of the ANC’s armed wing, and engaged in guerilla activities. He was deemed a terrorist by the government at that time that prevented him entering the United States until July 2008!
During his time in jail Nelson studied for another degree and wrote several books. As mounting criticism of the South Africans system of Apartheid mounted, the sitting government wanted to save face and they reversed their ban on the ANC and released Mr. Mandela after 27 years in jail.