Since 1980, in other words, the U.S. economy has transferred eight points of national income from the bottom 50 percent to the top 1 percent.

That trend is even more remarkable when you set it against comparable numbers for wealthy nations in Western Europe. There, the bottom 50 percent earn nearly 22 percent of the income in those economies, while the top 1 percent take in just over 12 percent of the money.

The income situation in Western Europe today, in other words, is similar to how things were in the United States nearly 40 years ago.

Those changes have made it easier for high-income Americans to grab more and more of the income pie in any given year.

From 1980 to 2014, for instance, the bottom 20 percent of earners in the United States saw their after-tax income rise by just 4 percent, according to the World Inequality Report. By contrast, the top 10 percent saw their post-tax income more than double over the same period.

Income gains at the tip of the distribution were even more extreme, with the top 1 percent nearly tripling their post-tax income and the top 0.001 percent realizing income gains of over 600 percent.

Western European countries, by contrast, took a different approach. “Continental Europe meanwhile saw a lesser decline in its tax progressivity,” according to the report, “while wage inequality was also moderated by educational and wage-setting policies that were relatively more favorable to low and middle-income groups.”

The income situation in Europe is a reminder that advanced economies don't need to be set up this way and that the growing gulf between rich and poor in the United States is largely a result of deliberate policy decisions.