America refused to join – the Senate was concerned America would be required to “police” the world and would get dragged into future disputes and wars
Germany and the other defeated powers were not invited to join until they had proven that they were responsible and trustworthy
The Soviet Union was not invited to join either – Communism was to be isolated as if it were a plague, though it did join in 1934 only to leave in 1939
It left Britain and France, both weakened by the war, dominating the League
Japan considered the League as a European club (its headquarters was in Geneva) mostly concerned with European matters
Japan (in 1933) and Italy (in 1937) left the League, and Germany which eventually joined in 1926, left too (in 1933)