If it comes to separation Russia will move fast on Alaska. There are just too many raw materials there if you're willing to dig them out. Their old ties in Cuba would offer a tempting move on Gulf Coast states. China & Japan will race for Hawaii as it offers a very strategic launching pad to the American continents. Though I think China would have their focus split between Hawaii & the west coast via Mexico. The plains states & east Texas seem the only likely areas to have little foreign competition for control.