DRÉ, Chad - So why is Africa such a mess? To answer that question, let me tell you about a 34-year-old man who limped over to me at this oasis in eastern Chad. "My name is Moussa Tamadji Yodi," he said in elegant French, "and I'm a teacher. . . . I just crossed the border yesterday from Sudan. I was beaten up and lost everything." Mr. Yodi, a college graduate, speaks French, Arabic, English and two African languages. During the decades of Chad's civil war, he fled across the border into the Darfur region of Sudan to seek refuge....