Treaty of Peace with Germany (Treaty of Versailles), 1919
President Woodrow Wilson was the primary architect of the League of Nations, an international peacekeeping organization that was the centerpiece of the Treaty of Versailles. The Senate rejected the treaty for ratification, and the United States never joined the League of Nations. The Senate did approve for ratification separate peace treaties with Germany, Austria, and Hungary.
Records of the U.S. Senate, National Archives and Records Administration
The Senate Rejects the Treaty of Versailles
The Constitution grants the president power to negotiate treaties with foreign governments, and gives the Senate the power to approve those treaties for ratification, if two-thirds of its members concur. The Senate has, at times, rejected treaties when its members felt their concerns were not adequately addressed. In 1919 the Senate rejected the Treaty of Versailles, which formally ended World War I, in part because President Woodrow Wilson had failed to take senators’ objections to the agreement into consideration.
They have made the French treaty subject to the authority of the League, which is not to be tolerated. If we ever are called upon to go to the assistance of France as we were two years ago, we will go without asking anybody's leave.
Senator Henry Cabot Lodge of Massachusetts, Letter to Senator Albert Beveridge of Indiana, August 11, 1919