Diagram is not intuitive, also highly misleading: Do it again with 1970 and 2020, or do a graph over time per country. Because social equality was MUCH better in between & the differences to today's inequality would stand out much more.
Anyone verified the data, could explain where it icomes from? Seems very dubious... How anything from 1820 can be measured accurately to start with...? let alone compare to 2020...?
I'm not sure it's accurate for all countries, especially outside Europe, but 1820 isn't prehistory and most European countries already had taxes and well-kept records.