Third world actually came from the cold war. There were the two major sides, but then there was a whole bunch of countries that weren’t really on either side. A whole “third world”. Of course, a lot of those countries were poor, so the term came to be associated with that, but there really isn’t a coherent definition of what it means to be a third world county. It has never really been about the standard of living for the average citizen though. More about whether a country is a bully or the bullied on the international stage, and we all know where the US falls on that spectrum.