After the destruction that WW2 left behind the nations of Europe were struggling to rebuild their economics and ensure their securities.
During the 1947's and 1948's events happened that the West European nations were getting worried about they securities and the United States encountered more of the Europeans problems
Which was in 1947's when the Cold War had began and the European problems that were happening was the Soviet Union as it was rising to power and in order to protect itself from being invaded it had taken over all nearby countries as a wall and had prisoners join the Soviet Union they were forced and this is the time when the United States was getting very worried they would keep gaining power and therefore a new organization was made.
As a result Harry S. Truman Created the North Atlantic Treaty Organization (NATO).