Piketty breaks this down in historic terms for all countries for which data is available in Capital and Ideology, tldr, a very small percentage of people have g

Piketty breaks this down in historic terms for all countries for which data is available in Capital and Ideology, tldr, a very small percentage of people have gotten much richer than everyone else for the last 200+ years, it's just gotten extreme after progressive taxes and regulations were rolled back in countries circa the Reagan/Thatcher years. I dunno if it's still up but the web page for the book had all the data.