Samantha Power in The New Yorker:
For the past two and a half years, the Arab-dominated government of Sudan has teamed up with sword-wielding marauders on horses and camels, known as janjaweed, to butcher, rape, and expel non-Arabs living in the western region of Darfur. In May of 2004, the United States, Europe, and Africa settled on an imperfect solution for stabilizing the region: send in the African Union. The A.U. accordingly dispatched sixty unarmed observers and three hundred “green helmet” soldiers to monitor a ceasefire between the government and the non-Arab rebels who were fighting it.
What followed was a textbook example of “mission creep.” The ceasefire collapsed, the Sudanese Air Force and the janjaweed continued their deadly raids, thousands more non-Arabs were killed, and the rebels began to splinter into rivalrous groups.
More here.