What Is the Difference Between First-, Second- and Third-World Countries?

First-world countries were originally North Atlantic Treaty Organization (NATO) members and their allies, second-world countries included communist-socialist states loyal to the United Soviet Socialist Republics (USSR) during the Cold War, and third world countries were undeveloped nations that didn't align with either bloc after World War II. The terms were created by French demographer Alfred Sauvy in 1952.