How did World War I contribute to the rise of dictators in Europe?

The outcome of the war left many people unhappy and the three most important dictators that arose were Mussolini, Hitler and Stalin. The Treaty of Versailles strongly punished the Germans which left them angry, and it was that anger that Hitler used to rise to power. On the other hand the US was not part of the League of Nations, thus they were relatively weak and could not enforce the law on the scale it should have.