The German elite stupidly continues fighting WWI into 1919 before seeking armistice. This causes a year like 1848, but with proletarian rather than bourgeois consequences. France and Germany for starters.
This strengthens the workerist and council communist left amongst the revolutionaries, but new strands of maximalist Social Democratic politics also appear, "centrist" in the terminology of the 20th century's revolutionary marxist left. There is a wave of opportunistic events both in terms of party factions and nations. There is a fair bit of blood where repressed national elites under the imperial system don't have the capacity to face France and Germany.
The IWW is much more difficult to crush, and in a multipolar world remains the preeminent US revolutionary tendency. It doesn't succeed of course, but there is an organisational continuity from 1905 through to the *US Depression.
I don't think Britain goes prior to the *US Depression. But I'm sure something (bloodier) than the General Strike occurs.
Socialism in Europe is split between competiting maximalist social democrats, "new style" statist centralist revolutionaries, councilist and workerist tendencies. With the multipolar German socialist situation, there's no chance of a slide away from democracy. The industrial area is large enough that there's no instinct for one man management. There are enough strong shops in Germany that noone is going to take the plants away from the workers, though they'll probably try to take their political power. The economic unit is large enough that areas like Turkey and China will fall under soft power influence. Some states, (Spain, South America) will be tempted to opportunistically take up these politics in order to control them—or use fire and bullets.
I'd say its enough of the world economy to cause the UK to fall to socialism during the next crisis, and, for Populist Laborism to gain a hold in US politics during the next capitalist economic crisis.
Soc.history.what-if already did this example in The Seed sequences of posts. (across a number of threads)
(Yes, I know this is the boring obvious example.—if someone can take Istvan Bibo's ideas of a Central European Commonwealth in 1956 and run them into a world socialist situation, good for them!)
yours,
Sam R.