I know CSA victories in the ACW have been done to death, but I want to join the party.
In this scenario, the Confederate States of America went to war wth the USA again in the 1890's, due to disputed territories where loyalty was divided, and they lost. By that time, the USA probably could have, at a great expense, reincorporated the whole of the CSA, but decided, as it was the general opinion at the time, that nothing of value was lost. Still, the CSA was severely punished, losing Tennessee, the Arizona territory, Oklahoma and Virginia (the CSA capital was moved from Richmond to Atlanta), and shortly thereafter, Texas seceded from the CSA and entered in the American Sphere of influence. The rump CSA left remained isolated and backwards, abolishing slavery as late as the 1920's and keeping racial segregation to this day, becoming increasingly authoritarian to keep the racial tensions from exploding, to the point that nowadays the Federal government is appointed by a military junta. Texas has been considerably more succesful, if worringly oligarchical. The USA is still one of the main superpowers, (though global power is more evenly distributed ITTL), and pretty much a social democratic country for our standards (Europe, OTOH, is more slanted to the right than IOTL).
There was a WWI in which neither the USA nor the CSA took part and which ended in a maintenance of the status quo. The main divergence in the world stage was a Communist revolution that started in Austria-Hungary and spread to Italy. It tried to turn the cluster of nations of the Balkans into the seed of a true international Socialist state, but the project stalled when Russia followed suit and decided to take a more ethnonationalist approach. For now, *Communism is doing much better than IOTL.
The Ottoman Empire still collapsed, if a bit later, after a series of Nationalist revolts led by the Arab population. A remarkable event was the emergence of a Syrian *Fascist pan-movement, leading to a Greater Syria that stainds against her neighgours and that counts as one of the most repressive states in the world. A Syrian inspired pan-movement gained momentum in Persia, that eventually went all Lebensraum on Central Asia. The Pashtuns and the Balochis didn't quite like this, and the Iranians decided that puppetizing them was cheaper than fully incorporating them.
China did much better, and Japan not nearly as good, but that allowed them to avoid their OTL mistakes and to keep a degree of power over East Asia.
This is generally speaking a richer but technologically a bit more backwards world, a world where nuclear weapons are a relatively recent developement, but the fear of a nuclear holocaust is still very present.