In 1993, after years of conflict between the Hutu and Tutsi ethnic groups in Rwanda, a new accord was signed and a UN peacekeeping mission was established. However, when Rwanda's and Burundi's presidents were killed in a suspicious plane crash in April 1994, civil strife erupted on a massive scale. Rwandan soldiers and Hutu gangs slaughtered an estimated 500,000 to 1 million people, mostly Tutsis and moderate Hutus, in the 100 or so days before the Tutsis regained power.
What has happened since?
Source: Rwandan Genocide Begins (1994) (http://encyclopedia.thefreedictionary.com/Rwandan+Genocide)