Hitler justified germany's aggression by stating that

Hitler believed that Germany required "Lebensraum" or more living space for the Germans and that this had to be through an expansion to the east.  After World War I Germany was, according to Hitler, humilliated and since the country reduced to a small state it that was threatened by his enemies in Europe, especially comunist countries.  

Under this context Hitler justified Germany's aggression to Czechoslovakia prior to WWII by saying he wanted to annex the Sudertenland, which were lands with a majority of German ethnicity and this way avoid comunist threats.  He used the Lebensraum belief (very popular in Germany  by then) to justify his need for expansion and to avoid the expansion of comunism.

He conviced the leaders of France, Great Britain and Italy to grant him this land and they did.  Later on Hitler invaded Poland.

can not you sorry