In The Increasingly Unequal States of America: Income Inequality by State, Mark Price and Estelle Sommeiller develop estimates for top income shares, from 1917 through 2011, for American states and regions. The national version of this story is now quite familiar: the iconic Piketty and Saez curve that starts high in the early years of the twentieth century (with the top 10 percent claiming about half of all income and the top 1 percent claiming about one-fifth), drops with the political innovations of the New Deal, and then climbs again—returning, by 2012, to its early-century heights—as those innovations are dismantled. So what does the state and regional breakdown tell us?
The full results are plotted below. For each year, the states (the light blue dots) are plotted by top income shares. The middle of the shaded box marks the median state (half are lower on the chosen measure, half are higher), and then the states are broken into quartiles: the middle quartiles (marked by the boxes) surround the median, the outer quartiles run along the lines between the boxes and the outer tick marks.
A few patterns stand out. First, the general sweep of the graph echoes the national story. The arc of inequality from Gilded Age to New Deal and back again is experienced across every state, not just in a few of them. Second, the policy innovations that dampened inequality—collective bargaining, retirement and unemployment security, labor standards, financial regulation, progressive taxation—also narrowed the variation across states. In the middle years of the last century strong federal policies trumped (or overcame) the economic and political differences among the states. And third, the erosion of those policies, beginning in the 1970s, saw both inequality and the variation across states widen again.