What were the consequences for the USA for rejecting the Treaty of Versailles and the League of nations?

The United States did not suffer any immediate aftermath for rejecting the Versailles Treaty and the League of Nations.  The United States signed a separate peace treaty with German in 1921, thus formally ending the war.  The United States was unable to alter the level of blame leveled at Germany since the chief negotiator, Woodrow Wilson, contracted Spanish Influenza while in Versailles--this gave the British and French more power at the treaty table as they...

The United States did not suffer any immediate aftermath for rejecting the Versailles Treaty and the League of Nations.  The United States signed a separate peace treaty with German in 1921, thus formally ending the war.  The United States was unable to alter the level of blame leveled at Germany since the chief negotiator, Woodrow Wilson, contracted Spanish Influenza while in Versailles--this gave the British and French more power at the treaty table as they could always point to their losses and say that they deserved reparations more.  As news leaked from the treaty conference that the victorious Allied powers were using the war as an excuse to add to their already-impressive empires, the American people also lost patience with the treaty negotiations, thus giving Senate Republicans more power to go against Wilson and his internationalism.

 The United States started to suffer for its isolationism during the 1930's.  Since the U.S. did not join the League of Nations, there was no country powerful enough to force Japan to abide by the Kellogg-Briand pact which denounced war as a method of settling disputes.  Japan left the League of Nations during its initial invasion of China.  The British and French were too busy with their own economic crises at home to notice German militarization.  While America was not truly isolationist, as it did host the Washington Naval Conference in 1921 and it led the Kellogg-Briand pact, its failure to join the League of Nations was a strong contributing factor to WWII, which was far more costly in terms of blood and treasure than WWI.