Nelson Mandela was a prominent anti-apartheid activist in South Africa, and he faced significant persecution from the South African government during the apartheid era. Specifically, he was arrested and imprisoned for his role in the struggle against apartheid, a system of institutionalized racial segregation and discrimination that was enforced by the National Party government from 1948 to the early 1990s.
Mandela was originally arrested in 1962 for his involvement in planning acts of sabotage against government installations. In 1964, he was sentenced to life imprisonment after the Rivonia Trial, where he and several other leaders of the African National Congress (ANC) were convicted of sabotage and conspiracy to overthrow the government. Mandela spent 27 years in prison, primarily at Robben Island, where he endured harsh conditions.
The South African government viewed Mandela and the ANC as a threat to their power and the apartheid system. His imprisonment became a focal point for the international anti-apartheid movement, and over time, global pressure mounted on the South African government to release Mandela and dismantle apartheid. After years of negotiation and growing opposition, Mandela was released from prison on February 11, 1990. He went on to play a crucial role in the transition of South Africa to a democratic society, culminating in the first multiracial elections in 1994, where he was elected as the country's first Black president.
In summary, the South African government imprisoned Nelson Mandela because he was a key figure in the fight against apartheid, and they viewed his actions as a direct threat to the maintenance of their racially discriminatory regime.