Many other countries were involved, including Japan and the USA (after 1917). The Empires of the Great Powers were also involved in the conflict which caused the war to widen into a World War.
The suffering of the participants in the Great War was so appalling, that when the war came to an end in November 1918, many hoped never to repeat such an experience again, and a mood of pacifism grew in the 1920s.
Britain, led by Prime Minister David Lloyd-George, was more sympathetic to Germany. Lloyd-George realised that if Germany was harshly punished this would cause great resentment amongst the Germans and could cause tensions in the future. He also believed that a strong Germany would be a good trading partner for Britain, and that a healthy German economy would prevent the rise of extremist parties either Communists or Fascists. On the other hand Lloyd-George had to listen to British public opinion which was calling for Germany to be 'squeezed until the pips squeak!'
The other great victorious power was the USA. Led by President Woodrow Wilson, the Americans had no great desire to punish the Germans. In January 1918 Wilson had proposed his Fourteen Points, which was a blueprint for a fair peace settlement at the end of the war. One of its main points was the idea of a League of Nations which would try to prevent major wars through negotiation. Wilson did not wish to punish the Germans, but at the Peace Conference he was overruled by Clemenceau and Lloyd-George.