I think we would have ended up with something very close to a full intergrated EU economically dominated by Germany with a few internal borders shifted around and a declining U.K. outside the EU.
Whatever, it would have been messy — very messy.
(However, the move towards social democracy in Germany was a thing pre-war, and if anything it was the capitulation to nationalism of the moderate left that opened the door to the radical left and communist fringe across Europe; it's interesting to speculate where things might have ended up if the standard bearer for hardline socialism had been someone like Rosa Luxemburg rather than Vladimir Lenin.)
I really do think the Great War broke the long slow march towards democracy and moderation that had started in the 19th C. Germany in the early 20th C was the centre of modernisation and Liberalism and if it wasn't for the war there is nothing to suspect that this wouldn't have continued.
There would still — probably — have been a round two in the 1930s or 1940s; WW1 was in some respects a revenge fight for the Franco-Prussian war of 1870-71. But without the gridlock of the western front to force the hothouse development of new weapons and tactics, the military tools of that second conflict would be much closer to those of our actually-existing WW1; that is, I don't believe we'd have ultimately avoided the bloodbathe of trench warfare — we'd just have postponed it (and retarded the development of civil aviation as an accidental side-effect).
The real question is whether the ancien regime would have survived (no collapse of the monarchies; the Hapsburg, Wilhelmine and Romanov dynasties survive into the second half of the 20th century, and those guys called Lenin and Trotsky and Hitler are just fringe radicals) and if so, what the consequences would have been further down the line. One thing's for sure: no European Convention on Human Rights!
(Source: lots of speculation here, but I'm an SF author with a track record in alternate history and this stuff is meat and drink ...)