The United States officially ended the war with the Central Powers in:

On July 2, 1921, U.S. President Warren G. Harding signed the Knox–Porter Resolution, which had been passed by the U.S. Congress and ended the state of war between the U.S. and Germany, Austria and Hungary, further setting the stage for bilateral peace treaties.

The continental congress made the federal government weak when it drew up the Articles of Confederations of the following:
* Created limited to the Central Government
*It had only just one branch
*Congress couldn't regulate trade, or tax so they had to ask the states