World War I ended largely due to the United States joining on the side of the Allies which convinced the Central Powers that defeat was inevitable. The Paris Peace Conference was called in which the "Big Four" Allied leaders would construct the Treaty of Versailles and formalize the terms of peace for the defeated Central Powers
The British and the French wanted to punish Germany so they could never wage war again and to get back what they spent to fight the war. Many groups that helped win were not included in the Treaty of Versailles for several reasons and it was primarily Great Britain, France, and the U.S. who decided what the post-WWI world would look like.
The League of Nations was one of the fourteen points which was actually followed, but because the U.S. Congress did not approve the country's admittance, the U.S. did not join it. Many of the other Fourteen Points were ignored completely.