The Danzig Corridor
The large portion in Brown is Germany. The smaller portion in brown on the right is East Prussia which was inhabited by Germans and ruled by Germany, as was West Prussia the Danzig corridor.
At the signing of the Treaty of Versailles in 1918 after World War I, 80% of those attending the signing were Jews. Germany was forced to give the Danzig corridor to Poland, a country that was controlled by the Jewish Bolsheviks, who 1939 began to slaughter the now isolated Germans living in East Prussia. After almost 60,000 Germans were murdered by the Jewish Communists, Hitler sent forces into Poland to save as many remaining Germans as possible.
Hitler did not want war to expand his borders or to build an empire. He wanted to save his German people from a massacre by the Jewish Communists in the land that had been stolen from Germany.
On the maps below, you can see how the German citizens living in East Prussia were isolated from Germany by the Polish Bolsheviks.