Interesting. Here I thought it had to do with the amount of industrialisation within a country’s GNP. “First-world” countries had a post-industrialised mindset to their culture, which assumed that if something was needed, that they would either produce it themselves, or pat to have it produced in a similarly industrialised country, “second world” countries were in an “industrialisation” mode — ie: they were still building up that infrastructure to be able to have the tools needed to produce needed items at scale, and the “third world” countries who were pre-industrial cultures due to either social taboos, lack of an educated populace or lack of resources.
That it was actually a political division from the 50’s and 60’s is an interesting concept which makes me wonder if there are further sub-divisions within that ideology… for those aligned with the commercial democracies, yet not able to keep their commercial industry, what “world” applies? Ex: Italy or the state of “California” (If it were to ever secede)?