In his blockbuster book Capital in the Twenty-First Century (2014) Thomas Piketty tries to answer this question. His conclusion? “Inequality with respect to capital is always greater than inequality with respect to labor.”

He means that across history, the top 10 percent of earners have taken 25-30 percent of all income earned from labor. But the top 10 percent of owners of capital have always taken at least 50 percent of all wealth, and in some countries 90 percent.

To put it another way, the bottom 50 percent of people in work earn between a quarter and a third of all labor income. But in terms of total wealth or capital, the bottom 50 percent often own nothing at all, or less than 5-10 of all national wealth.

Given the difference, Piketty argues that inequalities of income are almost reasonable, whereas “inequalities with respect to capital are always extreme”.

In the United States today, 10 percent of the people own 70 percent of all capital. In Europe, it isn’t much different: the top 10 percent own 60 percent of all capital, and the bottom 50 percent have 5 percent of all capital.

In Europe, a quarter of the population has wealth of 20,000 Euros at most. Another quarter have virtually no wealth at all, or more debts than assets. Most of this 50 percent are renters with no more than a few thousand euros in their account.

Yet it was once even worse. Before World War One, the bulk of Europeans worked their whole lives for a pittance for a people who never had to work. The wealthiest 1 percent of the population in France and Britain owned fully half of the nation’s wealth.

The rise of a propertied middle-class, comprising 40 percent of the population, was one of the great changes of the 20th century. This demographic gained a third of the wealth in Europe, and a quarter of it in the US. How did this shift happen?

Partly because the wealth of the top 10 percent was cut in half due to war, depression, and pro-labor government policy. Many more people now had to work, and wages became more important as the source of wealth.

Yet for most of human history, 10 percent of society owning most of the wealth was the norm. The rise of a big middle class in the 20th century may in time seem like a historical aberration.