THIS IS NOT ACTUALLY A NEW THEORY: There’s long been a theory that peacetime is bad for maintaining the global order — turns out a war now and then does a nation good. But this is a grim prognosis for the United States: “First, the viability of multiethnic states facing a less challenging external security environment will certainly decrease … [T]hose that survive will have to cope with a much higher level of ethnic separatism and demands for autonomy.”