In peacekeeping, the transition period is the most dangerous time. It is the time when the factions who have been at war vie for power, and when extremists try to make the most of the vacuum, to derail the peace and seize power. In the case of Rwanda, by the time the peacekeepers arrived it was already too late for peacekeeping.
On the face of it, the assignment was unambiguous. A three-year civil war had ended in peace, with a handshake between government and invading rebels. A more tangible peace was enshrined in the Arusha Accords, signed by the former enemies in Tanzania