Being a "what if?" we can't really know, but Nazism riding to power on the back of the Versailles treaty becomes an impossibility.
Exactly how Imperial Germany would have developed after winning and surviving WWI we can't know.
It could over a few dacades time have evolved into a full parlamentarian democracy with a constitutional monarch. Or there might have been some kind of reactionary political initative to squash such a dvelopment. In which case we could get a revolutionary socialist movement and perhaps a Marxist revolution.
It also depends on what happens outside Germany. There's no reason for either Italy or Spain not to go fascist — unless we assume German political and military dominance means there would be German armies propping up the regimes in these states. For how long? At what cost?
But is the German government good enough democrats to support say the Spanish republic here? Or is it some kind of reactionary clique preferring the phalanhists?
What's happening in Russia? Would there be a revolution? Would a victorious Germany go on fighting one indefinately over in the east if there was? Would it win a conflict like that?
What would happen to the Habsburg empire? The odds for it staying together in the long run weren't good. Would Hungary fight for its independance? To the north the Poles might, involving Germany more directly. If Russia is still in the game I think we can rely in it fanning variuos Slav national independance movements.
Or would Germany come up with some kind of winning formula for turning itself into the guarantee of some kind of new political entity, a kind of EU, where all kinds of regional and national entities could be given enough latitude to not try to break the edifice apart. But that would involve Germany willingly giving up massive amounts of direct political control gained in WWI.
The Ottoman empire would likely splinter in a million pieces in the end anyway. Would Germany involve itself? Or is this where France and Britain makes up for losses?
Does Germany take over French and British colonies? What's the relationship then with Japan and the US? Could there be a WWII involving Germany, Japan and the US (unknown alliances)? Or Britian, which would hardly have been eliminated as a colonial power?
How does Germany treat France? French revanchism is a foregone conclusion, but could there be some kind of cooling down and ideally a meeting of democracies? Or would it be France, perhaps rather than Russia, that went through a socialist revolution?
The world after WWI with Germany defeated didn't become peaceful. There's no real reason to assume it would have been anymore peaceful with a victorious Germany, though it would unarguably have been better for Germany, and in the long run would have had the added boon of no Holocaust.
But then again, how long would the US allow Germany to have things their way?
What if Russia doesn't have a revolution, modernises and industrialises successfully, and in 1939 we get the line up Russia, France, UK, Italy again fighting Germany over European supremacy, but with Russia as the major partner of the alliance holdimg both the manpower and wealth to take on a German dominated Europe?
Let's say Germany stays authoritarian as a result of winning WWI, at least for several decades to come, and the Habsburgs survive propped up by Germany. We have a political order in eastern Europe still based on large empires, but with scores of movements for national independance.
If further east Russia is revving up and hypothetically transforming itself into an industrialised democracy, possibly devolving parts of the empire into friendly allied states like the Ukraine, Finland, a kind of rump-Poland perhaps even.
In a showdown it might then be Russia that rolls in, breaks the German political dominance of Europe after WWI apart and establishes dozens of new independant nations.
Nationalism was an unsettled matter before WWI. The war did provide a kind of resultion, especially in eastern Europe. If Germany wins, this thorny problem would still have to be resolved — either by Germany granting enough independance, or by these movements taking Germany apart on their own, or them doing it with outside aid.
