The policy of appeasement that future Allied leaders like Chamberlain followed were critical in the expansionism and aggression that defined the Nazi rise to power. I think that there is an element in which one has to be careful from absolving Hitler from responsibility for what he and the Nazis did. However, appeasing Hitler and the Nazis played a significant role in the expansion and aggression that would come to define them. Consider the most basic definition of appeasement in this understanding:
the policy of settling international quarrels by admitting and satisfying grievances through rational negotiation and compromise, thereby avoiding the resort to an armed conflict which would be expensive, bloody, and possibly dangerous.
In the desire to avoid another protracted conflict, Chamberlain and others appeased Hitler. In surrendering nation after nation and in failing to recognize that the value of Hitler's promises in this realm was fairly worthless, European nations ended up aiding and feeding Hitler's aggression. I think that this becomes a rather critical element in that appeasement sought to avoid conflict, when conflict was both inevitable and the only possible solution to stopping the malevolence of Hitler and Nazi Germany. It is here where I think that the Allied policy of appeasement was responsible for feeding Hitler's expansionist tendencies.