I don’t see really see how it actually behooves anyone to go to war when fossil fuel reserves are running low, or about to.
There will certainly be a lot of chaos if that happens before we have other ways to transport food and other supplies around, though.
Same for all the other looming disasters caused by over-industrialization of everything, such as running out of clean water, running out of food, running out of ecosystems that can support our form of life, etc.