After the 1948 election victory of the Afrikaner-dominated National Party, which supported the apartheid policy of racial segregation,[23] Mandela began actively participating in politics. He led prominently in the ANC's 1952 Defiance Campaign and the 1955 Congress of the People, whose adoption of the Freedom Charter provided the fundamental basis of the anti-apartheid cause.[24][25] During this time, Mandela and fellow lawyer Oliver Tambo operated the law firm of Mandela and Tambo, providing free or low-cost legal counsel to many blacks who lacked attorney representation.[26]
Mahatma Gandhi influenced Mandela's approach, and subsequently the methods of succeeding generations of South African anti-apartheid activists.[27][28] (Mandela later took part in the 29–30 January 2007 conference in New Delhi marking the 100th anniversary of Gandhi's introduction of satyagraha (non-violent resistance) in South Africa).[29]
Initially committed to nonviolent resistance, Mandela and 150 others were arrested on 5 December 1956 and charged with treason. The marathon Treason Trial of 1956–1961 followed, with all defendants receiving acquittals.[30] From 1952–1959, a new class of black activists known as the Africanists disrupted ANC activities in the townships, demanding more drastic steps against the National Party regime.[31] The ANC leadership under Albert Luthuli, Oliver Tambo and Walter Sisulu felt not only that the Africanists were moving too fast but also that they challenged their leadership.[31] The ANC leadership consequently bolstered their position through alliances with small White, Coloured, and Indian political parties in an attempt to give the appearance of wider appeal than the Africanists.[31] The Africanists ridiculed the 1955 Freedom Charter Kliptown Conference for the concession of the 100,000-strong ANC to just a single vote in a Congressional alliance. Four secretaries-general of the five participating parties secretly belonged to the reconstituted South African Communist Party (SACP).[32][33] In 2003 Blade Nzimande, the SACP General Secretary, revealed that Walter Sisulu, the ANC Secretary-General, secretly joined the SACP in 1955[34] which meant all five Secretaries General were SACP and thus explains why Sisulu relegated the ANC from a dominant role to one of five equals.
In 1959, the ANC lost its most militant support when most of the Africanists, with financial support from Ghana and significant political support from the Transvaal-based Basotho, broke away to form the Pan Africanist Congress (PAC) under the direction of Robert Sobukwe and Potlako Leballo.[35]