He was convicted of Conspiracy to Overthrow the Government not Terrorism.
Hmmm...not quite.
First arrest was indeed for High Treason Against the State. An extremely serious accusation that carried the Death Penalty (as it did in the UK at the time). One charge was dropped and the remaining charges were changed to High Treason by advocating the use of violence against the state. This charge was brought under Martial Law that had been applied during severe rioting and looting that was taking place. Mandela was released when the case collapsed due to 3 of the Judges being National Party members, and the end of Martial Law.
His second arrest, and for which he served 5 years, was under the charge of Inciting Workers to Strike and with Leaving the Country without Permission.
His third arrest lead to a charge of four counts of Sabotage against the State and Conspiricy to Violently Overthrow the Government, what we would term Terrorism these days.
He also set up and headed the MK (Spear of the Nation), the armed wing of the ANC
He later admitted to 156 acts of sabotage taking place under his command.
He was in command of the MK during their bombing campaign in which cinemas, shopping malls, train stations, court rooms and so on were bombed, killing hundreds and maiming many many more, both black and white (I hate those terms) and he admitted he knew loss of life was taking place.
He approached the Chinese for weapons in a communist attempt to take power through violence
He accepted $60 million from Gaddafi and the Indonesian President (cant remember his name now) for weapons and training
He went to Ethiopia and trained in guerilla warfare for 2 months (it was meant to be 12 months)
One mans terrorist is another mans freedom fighter.........