First, Hitler had his country ready for war while the other countries were poorly prepared. Hitler used propaganda and other tactics to make the German people eager for war. He used their anger at the loss of WWI and their treatment under the Treaty of Versailles to make them want to get revenge and to regain their rightful (in their eyes) place as a major power. Meanwhile, the Allies did not want to have to fight another war. They were hoping for peace and were certainly not preparing for war. When the war came, Germany was ready while the Allies were not.
