You can say that Germany's aggressive expansion started at home. It began with the following steps.
- Hitler breaks the Treaty of Versailles by instituting a military draft and creating an air force.
- He remilitarizes the Rhineland where Germany was no supposed to have troops.
From there, Hitler went abroad. These steps included:
- Helping the fascists in the Spanish Civil War. He took no territory here, but he was helping an ally take Spain and he was getting practice for his military.
- The Anschluss with Austria.
- Taking the Sudetenland.
- Taking the rest of Czechoslovakia.
After that the next step was to invade Poland, which was the act that finally set off WWII.