Conversation so far:
What was the most risky activity Oliver Tambo did?
Oliver Tambo was directly responsible for organizing active guerilla units.
Was Oliver Tambo ever injured?
What was one of the attacks Oliver Tambo directed?
Oliver Tambo was the person who gave final approval for the 20 May 1983 Church Street bombing, which resulted in the death of 19 people and injuries to 197-217 people.
Where was one of the attacks Oliver Tambo orchestrated for Guerrilla activity?
The Church Street bombing was in the South African capital Pretoria.
Were there any casualties of the Church Street Bombing?
The Church Street Bombing resulted in the death of 19 people and injuries to 197-217 people.

Question: What was the reason for the bombing?
Self-contained rewrite: What was the reason for the Church Street bombing?