It can't be over-stressed just how horrible the first war was. France had six million casualties in a population of 40 million - 15 % of the population. Imagine today's USA having 50 million casualties in four years. How many people would want another war after that? Not to mention that basically all the towns along the north-east border had been destroyed. A century later farmers still find unexploded ordnance. It was tragic that Hitler exploited the reluctance of everyone else to fight again, but that reluctance itself was quite understandable.