Being a 1st, 2nd, or 3rd World Country depends on its Cold War orientation!
During the Cold War, countries allied with capitalist countries and NATO were known as 1st world countries. Communist countries and the Soviet Union were known as 2nd world countries. Third world countries referred to countries not allied with capitalist nations or NATO.
Third world became somewhat synonymous with underdeveloped and poor countries. It is now seen as politically incorrect to use the term “third world country.”