When compared to the United Nations, one of the main reasons the League of Nations was unable to fulfill its purpose was that the United States was not a member.
While the League of Nations was proposed by the U.S. President Woodrow Wilson, Congress voted that the US would not take part of the League of Nations. On the other hand, the U.N. was set up by Franklin D. Roosevelt, and the U.S continue to play a major role in the alliance.
Senator John F. Kennedy and Vice President Richard M. Nixon both pledged to strengthen American military forces and promised a tough stance against the Soviet Union and international communism. I hope this helps :)
I am thinking either the Battle of Saratoga or the Seige of Yorktown. I think the Siege/Battle of Yorktown because that was the last and decisive battle that ensured American Independence