Four factors in detail
The Treaty of Versailles
Created an anger in Germany that made many Germans support Hitler when he promised to destroy the Treaty. Also, it was so unfair that it undermined the confidence of western politicians to resist Hitler's demands, which many of them agreed with.
League of Nations
It was supposed to keep the peace, but it failed. It was too ambitious and badly organised. The group was betrayed by America, Britain and France and it was destroyed by Japan and Italy.
It is easy to argue that Hitler's actions pushed a Europe, which was desperate to be reasonable, into war. His invasions of Czechoslovakia and Poland went beyond correcting the mistakes of Versailles.
Some historians argue that Hitler would not have gone to war in 1939 if he had been faced with fighting Britain and France in the west and Russia and Poland in the east. Stalin gave Hitler the green light for…