On April 24, the Census Bureau announced how seats in the U.S. House of Representatives would be reallocated based on recent population data. There were some surprises. Texas gained two seats, and Florida gained one — fewer than predicted for both. California, for the first time, lost a seat. That New York lost a seat and Minnesota did not came down to the razor-thin margin of 89 inhabitants.

And yet, these unexpected results masked a more basic predictability, a geographical divide that has structured American life for over a half-century: Rust Belt vs. Sun Belt. Nearly all the states that lost congressional representation — Illinois, Michigan, New York, Ohio, Pennsylvania and West Virginia — hail from the old industrial heartland of the Midwest and the Northeast, while all the states that gained seats — Colorado, Florida, Montana, North Carolina, Oregon and Texas — are in the South and West. For all that has changed in American life during this period, this pattern has proved remarkably durable, as population and resources have consistently flowed southward and westward.

The term Sun Belt was first popularized by GOP strategist Kevin Phillips in his 1969 book “The Emerging Republican Majority” to describe the seismic transformation of the American South and West. Until the mid-20th century, these regions were the nation’s economic backwaters, “colonial” producers of raw materials that lagged far behind the rest of the nation in wealth and income. The South, in particular, remained impoverished, rural and agricultural. In contrast, the crown jewel of the American economy was the constellation of Northern industrial communities that stretched from the Eastern Seaboard through the Great Lakes to the Mississippi River.

In the 1930s, Franklin D. Roosevelt declared that the “South was the Nation’s No. 1 Economic Problem” and committed the federal government to ending the region’s age-old underdevelopment. New Deal programs like the Rural Electrification Administration brought power to the countryside, while federal wage policy fostered well-paying manufacturing jobs. The states, too, tried to address these issues. Mississippi launched its Balance Agriculture With Industry program in 1936, a groundbreaking experiment in government-sponsored industrialization.

The real takeoff point, however, came with World War II. The South and the West reaped a wealth of defense spending, becoming home to military bases, munitions plants and other wartime industries. Fearing the destructive capacity of aerial warfare and hoping to uplift depressed areas, federal officials dispersed military installations to less densely populated regions, which had the added benefit of cheap land and warm climates.