Yugoslavia, Rwanda, Liberia, Somalia, Azerbaijan, El Salvador, Northern Ireland, Lebanon, Cambodia – all provide bloody evidence that civil wars continue to have a powerful impact on the international scene. Because they tear at the very fabric of a society and pit countryman against countryman, civil wars are often the most brutal and difficult to extinguish – witness the American Revolution. And yet, civil wars do inevitably end. England is no longer criss-crossed by warring armies...