A betrayal of Germany and a national humiliation.
Step-by-step explanation:
Hitler believed that Germany had been betrayed by its leaders in surrendering in 1918. He felt a military victory was still a possibility.
He also felt that the extremely punitive measures on Germany contained in the Treaty of Versailles were humiliating and needed to be overcome.
Such attitudes were also related to his anti-semitism. He blamed Jewish financiers for starting the war.
These attitudes dominated Hitler's foreign policy from his re-occupation of the Rhineland and re-armament both of which broke the Treaty of Versailles, to his occupation of Austria, the Sudetenland and Czechoslovakia, and finally the attack on Poland which started World War 2.