Even in the Expanse it was more of a cold war between Earth and Mars, and a class war between the belters and the rest of the solar system. Globalization and the advent of planet-scale weapons have made relative peace and cooperation the more sensible option. The only wildcard is a sovereignty that has nothing to lose, a bitter history, and the power to exact real harm, and the closest we have to that in modern times is Russia. And the best way to avert this harm is to ensure no-one has nothing to lose.
But as I've said before on this forum, The Expanse isn't facts.
Of course it isn’t facts. But it more closely aligns with what we know of human history and nature than the belief that humans will ever be at peace with one another.
Also a fact is that we haven’t seen a hot war directly between two major economic powers since WWII. Quality of life and the global commerce that drives it has been trending upward for some time. Cooperation has simply been recognised as the more fruitful path, but a global scarcity of vital resources could change that equation though.
But as I've said before on this forum, The Expanse isn't facts.