First an interesting what-if....
If, in 1918, say, you could predict a German economic crisis in 15 years, who would you predict would become Chancellor? Adolf Hitler or Walter Rathenau?
WWII may have been inevitable, but Hitler was certainly not... nor, perhaps, was WWII's particular character....
As to Versailles, a major was that the treaty expressed a range of contradictory strategies for dealing with Germany, with the result that the signatory powers all had 'outs' allowing them to 'pass the buck' on enforcing it. It probably would have been a far better treaty were it the second Treaty of Portsmouth (New Hampshire) instead.
As to WWI... I tend to subscribe to the Dumkopf theory of history. Kaiser W was, needless to say, not the greatest diplomat. I think it is plausiblethat his particular gifts, along with his failure to reign in the German war planning engines, ensured that each of three possible wars occurred at the same time, much to Germany's strategic distress.
Granted, the growing power of Germany (and the fear that provoked in Sparta... er. France, Russia, and Britain) encouraged a degree of recklessness that Prussia avoided through the 19th century... But it is hard to imagine that there were not better opportunities to let slip the Schlieffen plan.... and, for that matter, better opportunities to maintain American disinterest during the course of the conflict.
George Kennan's book, the Decline of Bismarck's European Order
is an excellent brief against inevitability: http://www.foreignaffairs.com/articles/33496/fritz-stern/the-decline-of-bismarcks-european-order-franco-russian-relations
Kennan's caustic description of Bismarck's successors is probably one of the most erudite yet vicious depictions of Gilded Age statesmen I have encountered -- I just have a narrated version of the quote to hand, but you can get the gist.
"In introducing The Decline of Bismarck’s European Order, Kennan sharply and explicitly condemned the new policy elites of post-Bismarckian Europe with a vitriol belying mere historical interest. He lamented the "disappearance of the last of those men ... over whose personalities and activities there still hovered something of the atmosphere of the respective anciens regimes in which they had been reared." Against these older "eighteenth-century personalities" he contrasts a group of new "Victorians" "less secure in their values, more self-conscious," with a tendency toward political judgments marked "by a love for the intricate, the indirect, the oversubtle, the allusive, and above all for the pretentious, in place of the blunt, sometimes brutal, but usually elegant and impressive facility of their predecessors for getting to the heart of things." By comparison to their aristocratic forebears, these new Victorians were "uncertain, histrionic, overacted -- always with an anxious eye to the spectators." He continues to comment upon their financial embarrassments, their sexual habits and pecaddillos, and their "bulging bodies" and poor health. "They were, for the most part," he concludes, viciously, "overfed, oversexed, and underexercised."
I suppose if one is to descend into ad hominem, it is to be wished that one could do it with such elegance.... Needless to say, Kennan was a fan of Bismarck, but rather less impressed with the latter generation of 'statesmen'.
In general, Kennan was one of a number of 'realists' who would tend to question the necessity or inevitability of World War I -- Keegan and Michael Howard are probably part of that camp. Of course "no permanent enemies, no permanent allies, only permanent interests" is a signature realist view that runs entirely counter to the European alliance systems that fused the conflict(s) -- in both meanings of the term.
Keegan's World War I was widely viewed as a pot-boiler, btw.