“Close the border!” It’s the clarion call of anti-immigration advocates. And for most Americans, securing and controlling the border is a reasonable and even necessary right for a sovereign nation.

But in spite of its perennial popularity, border enforcement historically has failed to deter immigrants from entering the country and illegal immigration grew in concert with increased enforcement since at least the 1980s.

Now the tide seems to be turning (at least temporarily).

In 2007 the country’s number of unauthorized immigrants peaked at 11.8 million, according to the Department of Homeland Security (DHS). By 2009, DHS reported that the illegal immigrant population dropped to 10.8 million and the numbers for 2010 may show further reductions.

This is the first two-year consecutive decrease in illegal immigration in decades. Now the big question is: Why?

The consensus among many experts has been that unauthorized immigration is driven by economic conditions: Latin American immigrants are motivated by a combination of poverty and lack of jobs in their home countries and the abundance of jobs and higher wages in the United States. As long as there were jobs open in the U.S. and poverty persisted in Latin America, immigrants were not deterred by the militarization and dangers of crossing the border.

In fact, until recently, some experts indicated that the border enforcement escalation of the 1990s and 2000s actually led to fewer immigrant apprehensions as immigrants were pushed to more remote border crossings where there were fewer Border Patrol agents – Arizona’s Sonora desert, for example.

But in the past week, several analysts (and the DHS) have claimed that the reduced illegal immigration numbers are due to improved enforcement. Writer Edward Schumacher-Matos wrote in The Washington Post that “enforcement is working, something that many pro-immigration activists hate to admit and that restrictionists refuse to recognize.”

To bolster his claim, Schumacher-Matos notes the decline in the number of illegal immigrants: only 175,000 entered between March 2008 and March 2009 compared to 650,000 in 2005. He also notes that the Border Patrol recorded a 70% reduction in apprehensions last year.

While there is no reason to dispute the numbers, the logic is flawed. Lower numbers of illegal crossings doesn’t mean that the Border Patrol is all of a sudden more successfully deterring immigrants.

The drop in illegal immigration has coincided with another recent change in America: The Great Recession. Fewer immigrants are journeying to the U.S. because there aren’t as many jobs. About 60% of the jobs lost during the recession were in construction, manufacturing, and commerce – sectors that employ the majority of Latin American migrant workers. The unemployment rate for Mexican migrants in the U.S. peaked at 12% in 2009 and the poverty rate increased from about 20% in 2007 to 27% in 2009.

This type of news travels rapidly between immigrants in the U.S. and immigrant homelands in Mexico and Central America. If the prospects for economic advancement in the U.S. are dim, then potential immigrants will be less likely to leave their homelands and will bide their time until the U.S. economy improves.

Analysts’ findings that there has not been a mass exodus of undocumented immigrants from the U.S. back to Latin America support the argument that it’s a lack of jobs and not an overabundance of enforcement that has slowed illegal immigration.

Immigration research analysts also confirm that the main reason immigration has decreased is due to the recession, just as immigration has historically declined during most periods of high unemployment in the U.S. and surged when the economy creates jobs.

Although unprecedented enforcement certainly may be playing a part in deterring immigrants by making their lives more unpleasant in the U.S. and at the border, its role in the illegal immigration decrease is outweighed by the state of the economy and the lack of low-skill jobs typically filled by immigrants.

Originally posted at the Bread for the World Institute.