Ok so I reckon your best bet here is south africa, I'm not sure if you count its otl departure from the Empire as decolonization but with a pod before 1910 im sure you can make it fit your standards. Probably want a government that is going to acquire nuclear weapons and remain neutral in ttls cold war and hope for a nuclear exchange, even if US and Russia remain great powers european countries are quite possibly not in a state to remain so. leaves US, Russia, China, Japan, India and a Nuclear South africa in 6th place.