Tighter Border, More Control? Not So Much

Three decades of increasingly strict border controls not only failed to keep undocumented workers out of the United States; it also prevented them from leaving.

Despite all of personnel and resources allocated to border security, the monumental efforts have done little to stem the flow of illegal immigrants and have in fact backfired, according to a recent study published in the American Journal of Sociology. The escalation of border controls has not only been ineffective in stopping the entry of undocumented Mexicans; it has in fact prevented them from returning back to their home country.

Around 20,000 Border Patrol agents collectively made 337,117 arrests in 2015, detaining individuals who arrived in the United States illegally. The year prior, that number was 486,651, according to U.S. Customs and Border Patrol data (PDF).

Billions of dollars, hundreds of miles of fence, all varieties of surveillance equipment and more - all of which is most concentrated on the U.S. border with Mexico - are dedicated to the purpose to prevent illegal migration into the United States.

Immigration Fears Not New in US History: Photos

Between 1986 and 2010, the United States spent $35 billion on border security. That includes $2.4 billion spent on 670 miles of fencing, which covers about one-third of the entire border, created in accordance with the Secure Fence Act of 2006.

Over that same period, the net rate of population growth among undocumented immigrants doubled.

"Greater enforcement raised the costs of undocumented border crossing, which required undocumented migrants to stay longer in the U.S. to make a trip profitable," said Douglas Massey of Princeton University. "Greater enforcement also increased the risk of death and injury during border crossing."

'Longest' Drug Tunnel Found on Calif.-Mexico Border

Border security also made it more difficult for undocumented individuals to return home. What was once a cyclical flow of workers across the border has been blocked off, leading to a settled population of some 11 million undocumented residents in the United States, many of whom have been here 15 years or more.

What will likely stem the flow of undocumented workers isn't so much enforcement as changing demographics. Mexican families are having fewer children, and Mexico is increasingly home to an aging population, one less migration-prone. The same population shifts are occurring in other Central American countries home to migrants that transit through Mexico on their way to the United States.

The cost of building a barrier along the entire U.S.-Mexico border, a proposal favored by Republican frontrunner Donald Trump, has a price tag between $15 billion and $25 billion, at a cost of up to $16 million per mile, according to CNBC. The cost of maintaining such a structure would be around $750 million annually.

Video: Points-Based Immigration Systems

Hundreds of thousands of illegal immigrants are forced out of the United States every year, and since 2010, the majority of deportees are convicted criminals, according to government data. But according to a survey of deportees from 2012, 22 percent have children who are U.S. citizens and often left behind. This creates a powerful incentive for those deported to return to the United States.