A Thousand Hills: Rwanda’s Rebirth and the Man Who Dreamed ItBy Stephen KinzerJohn Wiley, 380 pages, $25.95In one great funnel of humanity, half a million refugees came down the road, all at once.

In April 1994, long-standing tensions between Hutus and Tutsis - the two main ethnic groups in the African state of Rwanda - exploded when the plane of Juvenal Habyarimana the Hutu president, was ...