By MICHAEL BARONE

http://online.wsj.com/article/SB10001424052748704111504576059843371291946.html?mod=WSJ_newsreel_opinion

After the initial results of the 2010 Census were released before Christmas, commentators focused on their short-term political effects and demographic implications. Many noted the six House seats and electoral votes that will be reapportioned to states carried by John McCain from states carried by Barack Obama. Others noted that California, for the first time since it was admitted to the Union in 1850, gained no new seats.

All well and true. But it’s also interesting to compare previous Census results to see how America has changed in the last 40 years, since 1970—and to compare it with how it changed in the 40 years before that. The comparison tells us much about the country’s present—and the shape of the future.

The years around 1970 were a flex point. We moved from the post-World War II industrial behemoth dominated by big government, big business and big labor to a nation reshaped by high tech and high finance. The decades-long farm-to-factory migration also drew to a close, while a period of unanticipated major immigration from Latin America and Asia began. The middle and late 1960s gave us the civil rights laws that successfully desegregated the South, and the lavish welfare spending and lax crime control that bedeviled the great cities of the North.

Population growth over the two 40-year periods was roughly comparable, 80 million or a 65% increase in 1930-70, and 105 million or a 52% increase in 1970-2010. But the way the country grew was sharply different.

Start with “Megalopolis,” the name applied by demographer Jean Gottmann in his 1961 book of the same name to the region that started in southern New England, centered on New York City, and ended in Washington, D.C. This was a boom area in 1930-70: The states from Connecticut south to Maryland plus D.C. and metro New York had a population increase of 69%, above the national average of 65%.

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Megalopolis was prosperous and a huge generator of jobs, but the boom described by Gottmann petered out as New York and other jurisdictions raised taxes to record levels, and an enlarged public sector squeezed the life out of much of private industry. New York City lost one million people in the 1970s, and growth in the region has been sluggish since, with immigrant inflow balanced by native outflow. Overall the region grew just 19% in 1970-2010, far below the national average of 52%.

Faring even worse was the “Foundry” (the term coined by Joel Garreau in his 1981 book, “The Nine Nations of North America”), stretching from upstate New York and Pennsylvania west to the Great Lakes states and the Mississippi River. Population there increased 49% in 1930-70, fed by farm-to-factory migration and the movement of one-third of American blacks from the rural South to the urban North in 1940-65. Big Three auto companies were still building assembly plants in Michigan and Ohio in the 1960s, just as industrial union membership was peaking.

But unionized factories have been poor competitors over the past 40 years, and high urban crime rates have wreaked huge damage in cities like Detroit. People have been outmigrating from the Foundry since 1970, and the region’s net population increased only 13% in 1970-2010, the lowest rate of any region in the nation.

And the West Coast? World War II brought GIs and defense workers to California and Washington, and afterwards many, attracted by the pleasant climate and open spaces, stayed and enticed others to follow. The population of the Pacific states including Oregon, Alaska and Hawaii tripled—up 208%—in 1930-70. But growth has since slowed. High taxes and slow-growth policies that raised housing prices are one reason. Latino immigrants have been streaming in but almost as many native-born have been moving out. The Pacific states grew 88% in 1970-2010, well above the national average, but far slower than in 1930-70 and slower than the South Atlantic states, Virginia, North and South Carolina, Georgia and Florida.

Those five states’ population doubled (up 102%) in 1930-70, but growth accelerated in 1970-2010. Black outmigration halted in the late 1960s and businesses were attracted by favorable public policies including right-to-work laws and low tax rates. The population of the South Atlantic states increased 114% in 1970-2010, and the 2010 Census shows that they’ve overtaken the five Pacific states in population, 50.7 million to 49.9 million.

The Rocky Mountain states, starting off from a low base, had a larger percentage population gain in 1930-70 (124%) and 1970-2010 (166%) than any other region. Phoenix, Denver and even Las Vegas have become nationally significant metro areas.

There also are signs of similar gains in the Great Plains, which languished in 1930-70 with only 23% population growth as farms emptied out. Growth there has picked up, at 26% in 1970-2010, with a perceptible acceleration in the last decade. Demographically, these two regions are starting to look like each other, with healthily or robustly growing metropolitan areas surrounded by lots of space.

Another area that was written off by demographers 40 years ago but that has come roaring back is the Interior South, the Southern states west of the South Atlantic and east and north of Texas. They grew 26% in 1930-70, nearly 40 points below the national average, but they have grown 39% in 1970-2010, only 12 points below the national average.

One reason is that black outmigration halted just as the 1960s civil rights acts were passed and enforced. Instead we have been seeing black in-migration in the South in recent years. The South has become a good place to do business. Alabama and Tennessee, with their non-unionized plants, have become major auto producers. Memphis boasts not only Graceland but FedEx. And with a low cost of living, the region is home to many retirement centers.

Finally there is Texas. In 1930 there were (rounded off) six million people in the Lone Star State versus 13 million in New York. In 1970 there were 11 million in Texas and 18 million in New York: Each had grown by about five million. But in 2010 there were 25 million in Texas and 19 million in New York.

Back in the 1930-70 period, liberal political scientists hoped and expected that America would become less like Texas and more like New York, with bigger government, higher taxes and more unions. In one important respect—the abolition of legally enforced racial segregation—that has happened. But otherwise Americans have been voting with their feet for the Texas model, with its low tax rates, light regulation and openness to new businesses and enterprises.

Today one out of 12 Americans lives in Texas—the same proportion that lived in New York City in 1930. Metropolitan Dallas and metropolitan Houston, with about six million people each, threaten to overtake our fourth largest metro area, San Francisco Bay (population about seven million), in the next decade.

In 1930 half of all Americans lived in New England, Megalopolis and the Foundry, and 40 years later 46% did. Now only one-third of Americans live in those three regions, the same proportion as live in the South Atlantic, Interior South and Texas.

Will those trends continue, or will the recession years around 2010 be seen as another flex point? It seems safe to say that the answer depends on public policy. As state and local governments cope with budget shortfalls and fiscal crises, they might do well to consider how their policies have reshaped America over the past 40 years.

Mr. Barone is senior political analyst for the Washington Examiner, resident fellow at the American Enterprise Institute, and co-author of “The Almanac of American Politics 2010” (National Journal).