In the USA, Woodrow Wilson had problems, such as the fact that in the USA the idea of a League was not at all popular.
The people of the USA thought that the plans for the League of Nations suggested sending its troops to settle every little conflict around the world. They wanted the USA to stay out of such disputes.
Wilson insisted that all the signatories to the Treaty should join the League. The League was also supposed to enforce the Treaty. Yet some Americans hated the Treaty itself. Many Americans were recent immigrants, There were millions of German immigrants who had never approved of the USA joining the war against Germany. They certainly did not want the USA to pop up the League as it squeezed reparation payments out of Germany. They wanted the USA to have no part in it.
Some Americans were worried about the economic cost of joining the League. They thought it would be as if the USA were signing a blank cheque. The USA would promise to solve all international problems regardless of the cost. Business leaders in particular argued that the USA had become a powerful country by isolationism…