Angus has some thoughts, here is one bit:
In my own research with Norman Maynard (trans-dimensional Bayesian mixture modelling alert!!), we find that in the 1950s and 1960s and most of the 1970s, there were two distinct groups in the global distribution of cross-country income, and there was a high degree of mobility from the poor to the rich group. Since the second age of globalization began in the 1980s, a new distinct group of super-rich countries has formed, the gaps between the poor group and the richest group have grown, and inter-group upward mobility has become a rarity.
There is more at the link, where he serves up a triple yikes.