> Meanwhile, many countries have gone from some of the world's most prosperous to countries people want to emigrate from (Argentina, Venezuela come to mind).

This is oft-repeated misinformation.

Latin American countries experienced massive growth in the early 20th century and large incomes from grain export. That income was distributed in a very unequal manner. And back in the day there were no reliable statistics of the huge segment of the population living in complete poverty, both in urban shanty towns with no census to speak of, nor the masses of agrarian workers living in systems not too dissimilar to slavery. Every economist who has dealt with the issue has mentioned frequently that economic time series extended that far back are mostly extrapolation and speculation, and much of it is not particularly rigorous in its methods.