DURING THREE visits to Darfur and neighboring Chad, I have been witness to the first genocide of the 21st century. In a displaced persons camp called Zam Zam, I met Halima, who described the day her village was attacked, first by Sudanese government bombers, then by the merciless, government-backed janjaweed militia. She said, "The janjaweed tore my baby son from my arms and bayoneted him in front of...