The “Umhonto We Sizwe” — “Spear of the Nation” was the military wing of the ANC. It began in 1961, a year before Mandela went to prison. It’s anthem, which Mandela sang publicly the day he was finally released from prison, was a song about killing white people.
“We the members of the Umkhonto have pledged ourselves to kill them — kill the whites.”
It was organised with the help of Mandela, and it announced its foundation with a string of bomb attacks, almost all against civilian targets.
Mandela was not actually the official leader of the ANC until much later in the 1990s, but he was always considered its most influential member.