Answer: The right for Germany to invade other nations
Explanation: In his auto-biography/manifesto, Mein Kampf, he mentions that he believes that a nation only has a "right to expand" once all of its peoples are within it. So for Hitler, once all of the Germans are in Germany, Germany has the "right" to invade other nations. The Sudetenland, the border region of Czechoslovakia had a significant German minority, and Austrians are ethnically German. So for Hitler to believe that Germany had the right to expand, he needed both of these regions. Not to mention that the Sudetenland also encompassed a large amount of Czechia's resources and manufacturing. Czechoslovakia and Austria also both had vast amounts of gold, used to boost the German economy and reward the higher ups in the NDSAP. In summary, because Germans live in Austria and Czechoslovakia, much like Russia's justification for invading the Crimean Peninsula