Tax is a huge part of the inequality story
This new study looks interesting. It compares five Anglo-Saxon countries that have relatively similar backgrounds and tax systems: Australia, Canada, New Zealand, the UK, and the US; and it looks at the relationship between taxes and top income shares. We haven't reviewed the paper in detail, but this conclusion is striking:
"The share of the very rich appears to be extremely responsive to changes in marginal tax rates. Over the period 1970-2000, we estimate that reductions in tax rates can explain between one third and one half of the rise in the income share of the richest percentile group."
It also contains a raft of other useful data and analysis, such as graphs showing the change in these shares over time (the graph in this blog is an example.)
As a reminder, outcomes of inequality are important too, of course: note in particular the book The Spirit Level, which demonstrates how a wide array of social outcomes are associated not with absolute levels of wealth or poverty, but on inequality.