I would first say that what happened with Russia, at least to me, did not seem inevitable even with hindsight. I don't think Romney had some keen foresight - more like a lucky guess.
I also don't really see the same happening with China, though it's of course possible. A sudden economic downturn could trigger a need for an external enemy and a conflict.
But a military conflict between the US and China just seems like an absurd fantasy. It'd how you end up with a nuclear war and the death of millions. I don't think the Chinese secretly want this in the long run. They want peace and more business and more wealth