This question about GDP per capita of major combatants before and after WWI made me wonder how these GDPs were distributed. Do we know the Gini coefficient (or a similiar metric) for the major combatants in the years around WWII?
This was part of the focus of Piketty's Capital in the Twenty-First Century. He prefers to measure income inequality by looking at the share of the top decile/percentile/0.1% in the national income. In general, the story is that inequality decreased sharply throughout the Great Depression and WWII, and continued on a downward trend until the late 1970s-1980s. Now, inequality is back.
Here is the income share of the top percentile in the Anglo-Saxon countries:
Here is the income share of the top 0.1% in the Anglo-Saxon countries:
And here is the income share of the top decile in a broader range of countries:
You have specifically asked about income inequality, and that is how I have answered. However, Piketty argues that wealth inequality is both more severe and consequential. The immense destruction of private property during WWII really cut into wealth inequality, but again, since the 1980s wealth inequality has been making a come back too.