Most importantly the USA because congress wanted to maintain a policy of isolationism. If they didn't join the league of nations then they wont get dragged into another European Conflict
The United States did not join the League of Nations primarily due to Wilson's strong will and unwillingness to compromise. 1) First, Wilson, a Democrat, ran the Executive branch of the government,...
Germany joined the League of Nations because they needed to be accepted back into the world; but not as a rebel. They also needed some kind of stability; even if it was only visual.