After returning to south africa from algeria in 1964, nelson mandela was

Arrested and imprisoned

Explanation:

Nelson Mandela was a South African revolutionary, political leader and philanthropist. Mandela served 27 years in prison because of his political ideas and activism. He was particularly involved in anti-colonial and African nationalist politics. Upon his release in 1990, Mandela became the President of South Africa, which made him the country's first black head of state and the first one to be elected democratically.

profound political, administrative, and social changes in the british isles.