During the economic boom of the late 1990s, about 3 million Mexican immigrants entered the United States, the vast majority of them illegally.

Between 2005 and 2010, a period that covers the Great Recession, the migration from Mexico was cut by more than half, to 1.4 million.

These numbers are significant for two reasons. First, they illustrate how the flow of people north is inexorably tied to the state of the U.S. economy. As important is the persistence of the migration even during an aggressive economic downturn.

The fact that almost 1.5 million Mexicans still ventured north when jobs were scarce and enforcement at the border acute, proves the United States will always draw migrants from our neighbor to the south. In other words, what demographers call the pull factor in migration persists. Its strength just fluctuates, depending on a host of factors.

The recent news that migration from Mexico has slowed or even declined is significant, if not historic. Based on the results of a study by the Pew Hispanic Center, it is clear more Mexicans returned to Mexico than migrated to the U.S. between 2005 and 2010.

To put that in perspective, the trend reverses 40 years of migratory history. During that time, 12 million Mexicans entered the U.S., about half of them illegally.

The net result is the first decline in the population of undocumented immigrants from Mexico in two decades. That is particularly significant for Texas, which is second only to California in the number of Mexican-born residents, legal and illegal.

Demographers attribute the decline to the poor economy, tougher enforcement at the border, an increase in deportations and involvement of violent Mexican drug gangs in human trafficking. The study notes the pattern could be reversed when the economy improves. Other researchers have found Mexicans driven to migrate will attempt many crossings, despite the new challenges.

Still, you don't have to be a demographer to conclude aggressive enforcement at the border and in the interior has altered the landscape. Although it was not its intent, the Pew study documents the impact of recent immigration policy, including laws that target undocumented immigrants at the state level as well as the dramatic increase in deportations. When you have 1.4 million people moving back to Mexico between 2005 and 2010 — including 300,000 U.S.-born children — the force at work is more push than pull.

Immigration is about the flow of people. It is a pressing policy question, one that remains unaddressed. This new study adds to our knowledge of the forces at work and should inform the national debate. Insisting the border is not secure, for example, is no longer a viable reason for not addressing immigration reform. Equally unsound is the belief that enforcement alone will push all illegal immigrants back whence they came. There are still 11.2 million reasons to think otherwise.

— Dallas Morning News