In the 1930s, Germany was openly violating the Versailles Treaty and building up their military on a massive scale. But World leaders at the time did not want to face the problem and sought only to appease Germany. They continued to believe that Germany's demands would eventually be satisfied without having to go to war. This, despite Hitler's
"Mein Kampf" clearly laying out Germany's plans for world domination and enslavement and/or extermination of "inferior" races.
This reminds me today of the situation with ISIS. They will never be satisfied with peacetime concessions. This can only end in total war.