I understand there is no definitive answer but I'm wondering if there is any consensus amongst historians on this issue. If World War II is considered to have been inevitable but the Treaty of Versailles is not the main factor, what other factors are involved?
I'll post an answer that I gave a little while back; in short, no, the Treaty of Versailles did not make WWII inevitable.
The two main arguments tend to revolve around Germany's actions before or after World War One. On the one hand, we have a form of the Sonderweg thesis put forward by A.J.P Taylor in his controversial work The Origins of the Second World War. This suggested that Hitler was not in fact a revolutionary, radical figure but was instead following the same expansionist aims of German leaders in the past, like Bismarck, Kaiser Wilhelm II, and Frederick the Great. Therefore, Hitler was simply taking up the cause of Imperial Germany, only under different auspices and ultimately with different results. He saw Hitler as having no long term plans himself, but as being maneuvered onto the war path by advisors from the old elite and the army.
The other argument, which stems in many ways from John Maynard Keynes polemical attack on the Treaty of Versailles (The Carthaginian Peace, 1919), takes a different view. Rather than seeing Germany as an aggressor, this takes the view that Germany was treated very poorly at Versailles, that it did not deserve the 'draconian' measures it received, and even extends to German interwar propaganda about 'War Guilt,' suggesting that Germany was not solely responsible for the War. The reparations placed an unacceptable burden on Germany, the Great Depression made it worse, and so the German people turned to Hitler to lead them, resulting in a Second World War.
Both arguments come up short, for a variety of reasons. To start with argument A, Hitler did have long term plans that were laid out in Mein Kampf, in his posthumously published Zweites Buch (Second Book), and in his speeches and 'Table Talk.' His aims combined the racist, social Darwinist ideas of Austen Chamberlaine with an expansionism that outstripped even the Kaiser and his followers. So claiming that a Second World War was inevitable because the Allies failed to prevent an inevitable second German bid for world power runs afoul of the fact that there was nothing traditional about Hitler's aims or statecraft.
The other argument runs a foul as well. Before Hitler even came to power, the Treaty of Versailles was dead in the water. The reparations were postponed indefinitely in 1932, and had been previously reduced from a chimerical figure of 132 billion marks to 50, then 40 billion, increased again to 118 billion to be paid by the 1980s and with foreign monetary aid, and then again to 40 billion, of which Germany paid 20 Billion in cash or kind. Reparations were a significant psychological burden, but in reality the Germans could have and nearly did pay in full. The issue of Germany's western borders was settled at Locarno in 1926, which also saw the beginning of German and Soviet military cooperation (thus undermining the military clauses of the Treaty), and Rhineland was due for full German sovereignty and the Saarland for a plebiscite in 1935-36. By 1929 Germany's economy had long since recovered and was returning to dominance on the continent, and Weimar democracy appeared to be here to stay.
It was the Great Depression, not the Versailles Treaty or a Sonderweg, that laid the seeds for WWII in Europe. The Great Depression was itself a product, in the American setting at least, of irresponsible monetary policies by the Federal Reserve, and so had little to do with WWI or an alleged German 'Special Path' (Sonderweg). WWII itself was fought with new countries and factions, with Romania, Italy and Japan being allied powers in WWI, and the USSR not even existing until shortly after WWI. Asia was a significant theatre in WWII whereas it wasn't in WWI, and the aims and actions of the Powers involved in WWII often differed significantly from their Great War predecessors/counterparts. The "Second Thirty Years War" Thesis is the product of many things, overly-deterministic historiography and Eurocentrism to name a few, and straight up Bad History.
Opinions differ but the popular/populist impression that Versailles made another war inevitable are in my opinion teleological.
Germany was managing its war debts fairly well- and renegotiating them in ongoing diplomatic and financial dealings- until the Depression. The far right had always relied heavily on exploiting the sense of shame associated with Versailles, its impositions and the 'war guilt' clause, but far right politics was not especially strong in Germany until the Depression ruined the savings of the middle classes and the opportunities for the working classes. It also had the effect of discrediting those who were finally getting Germany out of the shadow of Versailles, principally by borrowing from the US so US creditors would counter the power of Britain and France (who had their own problems with trying to maintain their exchange rates).
The Depression left the door open for populist right-wing authoritarians, and basically derailed Germany's transition from its traditional militaristic autocracy to a modern democracy. There is some parallel with this in Japan. Tooze and AJP Taylor are worth reading for some background on this.