We tend to think of rising income inequality as a 21st-century problem. A more equal distribution of wealth is normal, and the growing clout of the 1 percent is an anomaly.

The problem is that in the long arc of history, none of that is really true. For centuries, rising inequality has been the norm in the West — and it’s the relative equality of the post–World War era that is the anomaly.

To see why, check out this chart from Italian economist Guido Alfani. Alfani led a project to compile original data on economic inequality in six European countries — Britain, France, Italy, Spain, the Netherlands, and Belgium — between 1300 and 1800. He then combined original data with Thomas Piketty’s Europe-wide data on inequality between 1800 and today — and made a chart, published on VoxEU (the publication of the Center for Economic Policy Research think tank), showing the percentage of wealth owned by Europe’s top 10 percent over the past 700 years. It’s pretty stunning:

The chart shows the rich getting richer at a basically unbroken pace between 1500, when they controlled about 50 percent of society’s wealth, and 1914, when they controlled about 90 percent. That’s nearly 400 unbroken years of rising inequality.

In the whole chart, in fact, there are only two time periods where inequality declines — both of which coincide with major catastrophes.

“The Black Death, the most terrible epidemic in human history, affected Europe in 1347-51,” Alfani writes. “Afterwards the richest 10% lost their grip on between 15% and 20% of overall wealth. This was a long-lasting decline in inequality. The richest 10% recovered their pre-Black Death quota only in the second half of the 17th century.”

The other, sharper decline in inequality happened between roughly 1914 and 1950 — when World Wars I and II killed tens of millions of Europeans and destroyed dozens of cities and manufacturing hubs.

The upshot, if Alfani’s data is right, is that we need to start worrying even more about growing inequality. It suggests that there’s something about the deep structure of Western economies that tends to concentrate wealth in the hands of a small number of people. Alfani isn’t sure what that is, as his project is still in very preliminary stages. But his data strongly suggests that something is going on.

Now, it’s possible that democracy and the welfare state, relatively recent innovations, would redistribute enough wealth to counter whatever was going prior to 1914. But Piketty’s data suggests this isn’t so — that we’ve returned to the pre–world wars pattern of rising inequality even in countries like France with extremely robust welfare states.

Extreme inequality is bad in and of itself, in that it privileges the luxury of a handful over the welfare of the many. But we also know, from fairly solid empirical research, that it can seriously destabilize democratic political systems. People don’t like it when 10 percent of the people control 90 percent of a society’s wealth, and sometimes they choose to do something about it like — think, for example, of the 1917 Russian Revolution. Hyper-inequality can also cause the rich to destroy democracy — think about the 1973 military coup in Chile against President Salvador Allende, motivated in large part by opposition to Allende’s redistributionist policies.

Now, our current political turmoil — the rise of Donald Trump and the European far right — doesn’t really fit that pattern. Data suggests that supporters of these factions are more motivated by concerns over immigration and cultural change than inequality per se.

But that doesn’t mean we can dismiss the political risk caused by growing inequality. We have every reason to believe, looking at the long run, that inequality will continue to grow in the coming years — and the risks it pose will grow accordingly. The risks that poses, combined with those created by a white backlash to multiculturalism, are great indeed.