I Will Ask You Questions - Now with MORE fantasy ecology!

Imagine that most of the world were to suddenly have all of their energy needs met with renewable energy which requires minimal maintenance and is consistently functional, instantly obviating any reliance on fossil fuels. This would include cars (which are now all electric), house heating (all natural gas replaced with electric), etc. What would be the new primary source of international conflict, and how would America and China respond to it?

I honestly don't see a whole lot of major changes happening in the war department with the advent of unlimited renewable energy. The American military-industrial complex is going to continue to find excuses to justify its own existence, whether that means protecting us from terrorists, or getting rid of that dictator that we put in power 20 years ago, or whatever else works. As for the other dozens of wars going on in the world right now, I would say that almost all of them have more to do with ideological differences and internal power struggles than they do with resources of any kind. I'm looking at this list of ongoing conflicts right now, and I'm finding it difficult to pick out even a single one that might likely have been avoided/prevented if both sides had access to unlimited free energy. Certainly not any of the top five at least.

Personally, I think the big changes to wars aren't likely to come until we get to the inevitable near-future scenario where upwards of 90% of the human workforce gets replaced with friendly automatons. As more and more of the population becomes unemployable through no fault of their own, it in turn becomes harder and harder for the world to justify letting all of the lazy poors starve on the street, and one by one, the nations of the world begin to fall prey to the global scourge of Socialism.

The more optimistic part of me would like to believe that national militaries wouldn't have much need to still exist in a near post-scarcity society, but more realistically, I'd say that humanity probably still has at least one or two more huge wars left in it before they finally have to give up their murder toys for good. I don't really see there being any kind of lasting world peace though until all the armies of the world are officially united under one banner. (Or possibly a small handful of banners?) Ideally, this would be some sort of global United Nations-like peacekeeping force, and not a massive, dystopian world empire. I'm going to go with the former since it's much less depressing.

Anyway, at this point, humanity and its robo-friends can finally settle down and put all of that war nonsense behind them, focusing on more productive things, like medical science, space exploration, and cleaning up after all of those past wars we made. Things continue peacefully like this for a good while, that is at least until we finally pick up our first signs of intelligent life from other planets. At that point, humanity will proudly dust off all of the old Kill-droids, and will happily go right back to doing exactly what humanity does best. Shooting aliens in the eyestalks.

(Wait, sorry, I got distracted for a bit there. The actual answer to your question is that humanity's last great war will be fought over who gets the nicest vacation spots. The world's trillionaires sending thousands upon thousands of warbots to secure their claims to the world's nicest beaches and mountain vistas. These vacation spots will obviously all be completely destroyed within the first few weeks of fighting, in a grand display of cosmic irony. RIP in peace, all of Hawaii.)