IIRC, Czechoslovakia was taken because other world leaders were so foolish. Hitler kept saying "I just want one more piece of land, and I won't invade." "And another bit, this time, I promise I won't invade." He held armies on the borders and if they didn't give him the land he wanted, he would invade.

He got Austria by telling the Austrian Nazis to stir up trouble, he then sent in an army to be a "peacekeeper". His army just stayed there. And none fo the leaders seemed to care.