I don’t think the Germans were justified in starting WWII and would not support that argument. You are correct that other minority nationalities like the Hungarians and the Poles also did not like being oppressed minorities in the newly created Czechoslovakia which was Czech dominated. Did you know that when Hitler seized the Sudetenland for Germany, Poland and Hungary also reclaimed and took back bits of territory from Czechoslovakia? It happened. A lot of historians don’t like to talk about it because well.....its very inconvenient for the narrative that it was all and only Germany that had a problem with the newly created Czechoslovak state.
The ultimate monstrosity was Yugoslavia. Who thought making a nation out of Orthodox, Catholics and Muslims who all hated each other was a good idea?
The French thought rewarding the Serbs for starting WWI by giving them effective control over Slovenes, Croats and Bosniaks all of whom hated them was a great idea.