The underlying factor that allowed Adolf Hitler to come to power in Germany was anger over the aftermath of World War I. There were two aspects to this anger.
First, there was anger over Germany’s position in the world. Germans felt that they deserved to still be a major power. They were very angry about the way they had been treated in the Treaty of Versailles. They were angry because much of their territory had been taken from them. They were angry because they were not allowed to have a full military. These things made them want revenge and made them receptive to the sort of nationalist rhetoric that Hitler used.
Second, there was anger and concern over the economy. The German economy was devastated in part by the reparations imposed upon them after WWI and in part by the Depression. The terrible economic times also helped to make people more receptive to extreme ideas such as those that Hitler espoused.
Conditions of extreme stress in a society often lead people to accept ideas and leaders they would not ordinarily accept. This was the case in Germany in the early 1930s.