Well, I wouldn’t go so far as to say France started WW2 - but the Treaty of Versailles definitely placed the Foundation on which the Nazis were able to build their regime.
It was a major factor causing the frustration for many Germans and left them, together with the Depression, longing for a strong hand that would lead them out of this low - a strong leadership that the NSDAP offered them.
Of course you could say that it didn’t become a World War until England and France declared war on Germany - but where they really given any other choice? They promised Poland to protect them against an ever bolder growing Nazi Germany, and they couldn’t just go back to that promise.
It would have been a political disaster not only for the foreign policy but also for the interior. What would the French and English people think of their Governments letting that Germany gain more and more territory, especially since just 20 years ago, they had already shown them once who’s the boss, why not put some pressure on them?
I do not believe that either the French or the British really expected the Germans to have the Military Juggernaut they had, and maybe they were even hoping that Hitler would back off once they showed him they were serious. (A huge miscalculation if they really expected that, though it would explain the rather …‘symbolical’ French invasion of the Saarland)
Did the French and English declarations of war turn the German war of expansion into the Second World War? Probably. Does that mean they started it? Definitely debatable.
I, for one, don’t think Britain and France really had any other choice to declare war on Hitler’s Germany. What bigger favor could the Western Powers have done to him than let him expand his Germany? The confrontation would have happened sooner or later, absolutely no doubt about that in mind, the French had humiliated Germany too much after WW1, and I think both France and the UK knew that.
They only question that was left was whether the war would happen now, or later, when Germany had possibly already expanded into the East and the Balkan, adding a couple million people to its manpower and maybe had even defeated the Soviet Union.
Every nation Germany could annex would strengthen it, but every nation it had to conquer and occupy would weaken it. So even though the timing might not have been the best (especially for France, cough, cough), I believe that an open confrontation with Germany was necessary.
It all would have been in vain, though, had Japan not pulled the US into the war. The UK fought bravely, but without the American aid, they would have had to make peace with Germany sooner or later, no matter how big Churchill’s speeches were.