1. The Treaty of Versailles
The Treaty of Versailles forced Germany to pay for all of the damage they caused, which was more than they could afford at the time, thus causing them to print more money and cause hyperinflation, leading to the rise of Hitler in the country's economic depression.
2. Rise of Communism
The Russian revolution happened a little while later, when Lenin rose to power and essentially forced communism onto Russia, which made then become the Soviet Union and leave the Allied Powers when WWII came around.
3. De-glorification of Warfare
Trench warfare was introduced during this time, as well as poison gas, which sharply turned war from a noble, honorable event into a disgusting and horrendous zone of terror. Bodies littered carelessly throughout trenches desensitized people to death and war, and war became less of an honor and more of a terror.
(hope this helped!)
