We need a good war to sort society out. Nothing like a bit of national service to build backbone.
What would be left after it? Theres never been a good war only bad ones.
Americans and Chinese are hopefully too intelligent to have a massive blast at each other, although there may be local wars I doubt if they will change anything really.
Next thing is going to be either a natural disaster or a change to alternative power sources, renewables and hopefully within 50 years fusion.
Some form of worldwide agreement on population control would be nice but I dont see it happening.