The Truman Doctrine led to the establishment of:

NATO 

The correct answer is option (1) - NATO

The Truman Doctrine led to the establishment of NATO (North Atlantic Treaty Organization). NATO was founded in 1949 as a collective defense alliance among Western European and North American countries to counter the threat of Soviet expansionism

The Truman Doctrine was a significant Cold War foreign policy initiative introduced by U.S. President Harry S. Truman in 1947. It aimed to contain the spread of communism, particularly in Europe. Truman argued that the United States should provide economic and military assistance to countries threatened by communism.