Rwanda is landlocked and dirt-poor, a bit larger than Vermont and a bit less populous than Chicago, a place so dwarfed by neighboring Congo, Uganda, and Tanzania that for the sake of legibility its name has to be printed on most maps outside the lines of its frontiers. As far as the political, military, and economic interests of the world’s powers go, it might as well be Mars. In fact, Mars is probably of greater strategic concern. But Rwanda, unlike Mars, is populated by human beings, and when Rwanda had a genocide, the world’s powers left Rwanda to it.