America and the West v. Russia, the East, and former Soviet Union (because Russia will bully them into assisting)
And I think China would stay out of it. Because it doesn't benefit China to emerge onto the global stage that way. I would expect increasing levels of involvement by the two main sides through increasingly intense proxies until someone fires a bullet in the wrong place at the wrong time. Hot spots will be the middle east, the ukraine (which is mostly stable now, thank god), and Afrika. As the two sides wage war I believe China, rather than deploying into the conflict, will instead sit back and increase presence in bordering nations of SE Asia, Central Asia, the Pacific, and others "for thier protection" much as other leaders havedone before. "These are ethnic Chinese people, they need out protection!" "these are small, defenseless nations, they need our military presence and government advice while we station the occupation forces"
So while Red and Blue fight it out, China is just going to expand their sphere, harvest the resources, solidify bonds, and grow and grow their war machine. Then, when the smoke clears and if no one has bombed and dragged China into the firefight like an idiot, then we will see a new world where China is on equal footing, if not ahead of, the next world power. Small nations in the pacific and around Asia and Afrika will begin looking to China for military aid instead of the United states who is now far away and a shell of the military might it once was.