The casus belli of Congress pulling their knickers up and fucking the world about the peace for Versailles Redux. They wouldn't tolerate being dictated to make peace. FDR gets impeached over being forced to sign.
All in all, *shrug* whatever... The AI sucks. We know this. The eight SUBRONs laying at the bottom of the Pacific along with X number of Japanese merchies don't matter much. Apparently neither does the funding of, what basically a quarter to a third of the world's industry? So, all in all, Congress is probably either going to sink the peace and we maybe get an armstice cold war sort of non-resolution or the US goes even harder into isolation this time.
I think this is the most likely. A lot of the factors that drive the Cold War aren't really present here, which should actually be a concern as this means a future WW3 is far more likely, as there are still several global powers which are relatively independent of one another - no NATO vs. Soviet bloc here despite Turkish proclamations of friendship. The only questions is who's going to start it, as right now none of those five major powers are interested in more than some border conflagrations. If any of the five remaining great powers take a turn towards (more) nationalism and start getting really greedy then we may have something. That aside, I think the most likely result is a return to the late-Victorian era for the time being, in the sense of a cluster of great powers balancing he world between them.
Certainly I think the New Comintern is the only big power bloc in the world, and whilst it is inherently expansionist, its already won in the areas the rest of the world might contest (western Europe).
I doubt the exhausted British who have to now deal with the consequences of letting their empire do all the fighting whilst they were safe and rich on their island (no bombing or ship loses though so their economy is probably great) are going to stop or care about the Turks digging into the middle east.
The French are more than likely to be our friends, not just because we surround them but because we agree ideologically (they almost certainly will elect a left wing government). Might even join one of the lesser spheres of the New Comintern voluntarily later on.
Japan has so much to do in China that they can't do anything else for decades, esepcially with the fear that doing anything in the Pacific at all will set off the US.
The US meanwhile is super wealthy and powerful, and could easily slide into isolationism now they have no real ties to the rest of the world. 'The West' is literally just the anglosphere at this point, and the UK is still a pretty powerful if declining imperialist power. I suspect if Russia respects the Monroe doctrine (which will no doubt be tested by communist revolutions), there will be little trouble for a decade at least...maybe when nukes are developed.
Leaving us with Turkey and Russia. Now...they aren't quite ideologically unified yet, however inertia and momentum of war comradeship, and winning an equitable peace between them will no doubt keep things smooth for a long time. There is no border tension, no outstanding dispute and no real sphere overlap (except allowing Russian ships through the straits into the Med, I guess).
Personally I think either Turkey will move closer into the New Comintern and do well there, or try to stay out of it and struggle with their absolutely massive far flung land empire for a few decades before some of it inevitably starts to split.
However, the future is looking pretty bright for the world, esepcially Europe.