The draconian terms of surrender left them feeling they had nothing to lose, humiliated and angry.
Cornered rat.
Giving them the Sudetenland emboldened them.
A few baby steps from there and pretty soon the whole world is involved.
That plus Europe was tired of war having lost so many during The Great War. Twenty years was not long enough for wounds to heal. Rest of Europe just didn’t want war again. Peace in our time and all that.