One event that motivated Nelson Mandela to turn to more radical means of changing South Africa during Apartheid was the Sharpeville Massacre of 1960. At this point, Mandela was already a long-time member of the ANC, or African National Congress, formed to fight against Apartheid, and he had been arrested in 1956 and tried (but acquitted) on the charge of treason.
In the Sharpeville Massacre, the police fired on protestors who were peacefully demonstrating against pass laws, and 69 people were killed. In the aftermath of the event, the country was convulsed by riots and unrest. The Sharpeville Massacre had motivated him to turn to new means of creating change. In 1961, Mandela became the founder and leader of Umkhonto we Sizwe (Spear of the Nation), a paramilitary wing of the ANC. In 1962, Mandela was jailed for 5 years for instigating a workers' strike, and the following year, he was arrested in the so-called Rivonia Trial for threatening to overthrow the government. Sentenced to life in prison in 1964, he served 27 years before his release. He went on to serve as President of South Africa.