Explanation: During the Rwandan Genocide in the 1990s, a UN peacekeeping force was actually stationed in the country, and tasked with... well, keeping the peace.

... but given no power to do so. The leaders of the force itself pleaded for a wider mandate to be granted by the UN Security Council, so they could actually do something to protect refugees from genocide, but only New Zealand went to bat for them. Their rules of engagement - the conditions under which soldiers are allowed to actually fire on the enemy - were so restrictive that there were incidents where UN troops were killed by enemy fire and still not allowed to fire back. For obvious reasons, the Tutsis, who were being genocided, thus did not fare much better under UN 'protection' than without it.

It is widely considered one of the UN's biggest failures.