Answer:
Hitler used the concept of nationalism to join all the German people from different nations in its neighboring countries.
Step-by-step explanation:
After the first World War, Germany forced to sign the Treaty of Versailles, which somewhat shattered the country in every aspect. The German Empire was broken in portions and formed into other countries.
Some of these countries became Czechoslovakia (Sudetenland), Silesia, Poland, etc. These areas had a large German population in them, and they somewhat lost their jobs. In the 1930's Hitler used the term nationalism in Eastern Europe to join all Germans together with land, which once was part of the German Empire. He invaded Czechoslovakia and towards western portions of Poland. Nazi used the slogan called Ein Volk, ein Reich, ein Führer.
Ultimately all this did not conclude as a good sign for the British and France, and at last, they declared war on Nazi Germany.