On 11-11-1918 WWI came to an end. This did not mean there was peace again.
In 1919 the peace was negotiated at the Paris Peace Conference.
During the conference the US, UK, Italy and France decided on the future of Germany.
Surprisingly Germany was not allowed to be present at the Paris Conference.
On 28-06-1919 the Treaty of Versailles was signed. Germany was forced to sign this.
The countries blamed Germany of the WWI. Therefor Germany was punished. They were not allowed to have a large army, needed to destroy weapons, give up colonies, territory and Alsace-Lorraine. On top of that Germany needed to pay for the damage caused by the war,