When the treaty of Versailles was agreed it had blamed Germany as the country who had lost and started the war and therefore had to be punished severely. The Germans didn’t agree with this, they expected to be treated as equals but the allies had won the war and were now superior to the Germans. They had no choice but to sign the treaty. The Germans had to surrender their army and were forced to reduce their navy. This was unfair because non of the other countries were ordered to do this. Germany lost 10% of its land and 12.5% of its population were now living in other countries. Germany also had to pay £6.6 billion in reparations which was a huge amount of money at the time. 16% of its coalfields and half of its iron and steel industries were lost. Germany had no say in any of these consequences and we basically forced to surrender what they had worked for for years.
In WWII the americans helped form the UN which is an international governing system that sets world laws on war. After developing this group of nations tjey formed together to destroy the german military.