Opposition to The League of Nations Treaty 1920; Flickr Commons
After WWI, the “war to end all wars”, anti-war sentiment was strong and President Woodrow Wilson promoted the idea of the League of Nations to avoid future conflicts. Despite his vigorous support, opposition by Republicans in the U.S. Senate was fierce, and the USA did not join the League of Nations which was established in October 1919.
The Empire of Japan joined the League in 1933.