Geopolitically, there isn't a balance of power that favors a regime that would challenge America and her allies.
You have countries like China and Russia which could possibly challenge the US in a WW3, but their interests aren't too similar to support a war against America. After all, China released a tactical nuke on Russia, so I don't think they'd be seen as allies.
Likewise, with China, you have other blocs of power in that region to counteract them, mainly other nations in ASEAN.
However, I think that we may see some regional wars that can have deadly consequences:
Iran-Israel. If Iran does get nukes, then there will be a deadly exchange. I read an executive report a few months back about game theory on such a war. If Iran attempted to strike Israel, there would be roughly 25 million dead civilians and leaders in a matter of a day.
Koreas: Although peace seems to be forthcoming (hopefully), there always exists the chance of an exchange. Even if it was conventional, millions would die. Seoul is just a few miles from the DMZ, and within artillery range from the DPRK.
US-Mexico: A less likely one, but I read a security report about US-Mexican relations. The author (who used game theory to predict most of the 20th centuries conflicts) states that by the mid part of the century, there will be a war between the US and Mexico, resulting in millions of deaths on both sides of the fence.
Back from the dead, I'm afraid.
