First World: developed natural resources

Second World: undeveloped natural resources

Third World: no natural resources

Of course, as Paul Simon famously said, “When I think back of all the crap I learned in high school, it’s a wonder I can think at all.”

I’ve seen “First World” in recent memes, and “Third World” is just a synonym for “poor” nowadays. I don’t recall ever seeing “Second World” used anywhere.

Were there intermediate Second World countries that just never came up?

Obviously, yes, but as a rule not called so, curiously enough.

His usage was a reference to the Third Estate (tiers état), the commoners of France who, before and during the French Revolution, opposed the clergy and nobles, who composed the First Estate and Second Estate, respectively (hence the use of the older form tiers rather than the modern troisième for “third”). Sauvy wrote, “This third world ignored, exploited, despised like the third estate also wants to be something.”

In the context of the Cold War, he conveyed the concept of political non-alignment with either the capitalist or communist bloc.

And if you happen to not believe in «the capitalist or communist bloc» as anything more than yet another layer of proxy civil wars in the same conjoined structure, mapping this on Estates of the Realm becomes even more straightforward, and rather brilliant.