1. Allied anger and desire for revenge. The First World War had been a long and bloody conflict, and the Allied Powers (France, Britain, Italy, and the United States) were understandably angry at Germany for starting it. They felt that Germany should be punished for its aggression, and the Treaty of Versailles was seen as a way to do that.
2. The need to weaken Germany. The Allied Powers were afraid that Germany would start another war, so they wanted to weaken it militarily and economically. The treaty did this by reducing Germany's military to 100,000 men, banning it from producing certain types of weapons, and forcing it to pay large reparations to the Allied Powers.
3. The desire to create a new world order. The Treaty of Versailles was also part of an attempt to create a new world order based on the principles of democracy, collective security, and self-determination. The Allies believed that by punishing Germany and promoting these principles, they could prevent future wars.
4. Pressure from public opinion. In the aftermath of the war, public opinion in the Allied countries was strongly in favor of a harsh peace treaty with Germany. The Allies were under pressure from their own citizens to make Germany pay for the war.
5. Lack of German representation. Germany was not allowed to participate in the negotiations for the Treaty of Versailles. This meant that the Germans had no say in the terms of the treaty and were unable to defend their interests.
The Treaty of Versailles was a controversial document that had a major impact on the course of history. It is often blamed for helping to cause World War II, as it left Germany humiliated and resentful. However, it is important to remember that the treaty was a product of its time and it reflected the views of the Allied Powers at the end of the First World War.