Where are Americans moving, and why? Timothy Noah, writing in the Washington Monthly, professes to be puzzled. He points out that people have been moving out of states with high per capita incomes -- Connecticut, New York, Massachusetts, Maryland -- to states with lower income levels.

“Why are Americans by and large moving away from economic opportunity rather than toward it?” he asks.

Actually, it's not puzzling at all. The movement from high-tax, high-housing-cost states to low-tax, low-housing-cost states has been going on for more than 40 years, as I note in my new book Shaping Our Nation: How Surges of Migration Transformed America and Its Politics.

Between 1970 and 2010 the population of New York state increased from 18 million to 19 million. In that same period, the population of Texas increased from 11 million to 25 million.

The picture is even starker if you look at major metro areas. The New York metropolitan area, including counties in New Jersey and Connecticut, increased from 17.8 million in 1970 to 19.2 million in 2010 — up 8 percent. During that time the nation grew 52 percent.

In the same period, the four big metro areas in Texas — Dallas, Houston, San Antonio, Austin — grew from 6 million to 15.6 million, a 160 percent increase.

Contrary to Noah’s inference, people don’t move away from opportunity. They move partly in response to economic incentives, but also to pursue dreams and escape nightmares.

Opportunity does exist in the Northeastern states and in California — for people with very high skill levels. And for low-skill immigrants, without whom those metro areas would have lost rather than gained population over the last three decades.

But there’s not much opportunity there for people with midlevel skills who want to raise families. Housing costs are exceedingly high, partly, as Noah notes, because of restrictive land use and zoning regulations.

And central city public schools, with a few exceptions, repel most middle-class parents.

High taxes produce revenues to finance handsome benefits and pensions for public employee union members in the high-cost states. It’s hard to see how this benefits middle-class people making their livings in the private sector.

Moreover, Noah’s use of per capita incomes is misleading, since children typically have no income and many in the Northeast and coastal California are childless. If you look at household incomes, these states are far closer to the national average.

As economist Tyler Cowen points out in a Time magazine cover story, when you adjust incomes for tax rates and cost of living, Texas comes out ahead of California and New York and ranks behind only Virginia and Washington state (which like Texas has no state income tax).

Critics charge that Texas’s growth depends on the oil and gas industries and is weighted toward low-wage jobs. But in fact, Texas’s low-tax, light-regulation policies have produced a highly diversified economy that from 2002 to 2011 created nearly one-third of the nation’s highest-paying jobs. In those years, its number of upper- and middle-income jobs grew 24 percent.

Liberals like Noah often decry income inequality. But the states with the most unequal incomes and highest poverty levels these days are California and New York. That’s what happens when high taxes and housing costs squeeze out the middle class.

As Noah notes, “Few working-class people earn enough money to live anywhere near San Francisco.”

This leaves a highly visible and articulate upper class willing, in line with their liberal beliefs, to shoulder high tax burdens and a very much larger lower class, many of them immigrants, available to serve them in restaurants, landscape their gardens and valet-park their cars.

There’s nothing wrong with living in a high-rise, restaurant-studded, subway-served neighborhood (I do). It’s great that America offers more such options than one and two generations ago.

But it’s foolish to try to cram everyone into such surroundings, as the Obama Department of Housing and Urban Development (as Terry Eastland reports in the Weekly Standard) and California Governor Jerry Brown are trying to do.

Noah notes correctly that fewer Americans have been moving recently. That’s always true in times of economic distress (the Okies’ trek along U.S. Route 66 to California’s Central Valley in the 1930s was a memorable exception, not the rule).

But they continue to move to the low-tax states that are providing jobs and living space where they can pursue their dreams and escape places that burden them with high costs and provide few middle-class amenities in return.