The USA was never was a member of the League of Nations, so to answer your question nothing different would have happened because they never joined.
Americans opposed joining the League of Nations because they didn't want America to be involved with other countries' affairs.
The other nations lost some confidence in the league
The U.S not joining.
League of Nations
President Woodrow Wilson tried to get Congress to approve the US entry into the League of Nations. The League of Nations was the predecessor to the United Nations.
Disbanding the League of Nations.
Could not get congressional approval
Americans opposed joining the League of Nations because they didn't want America to be involved with other countries' affairs.
The Senate
Woodrow Wilson
joining the league of nations
Woodrow Wilson proposed a League of Nations at the Paris Peace Conference after World War One, but the United States never ended up joining it.