An often-overlooked piece of the border security debate is the flow of guns from the U.S. to Mexico and into Latin America.

The thousands of immigrants who have been coming across the U.S.-Mexico border in recent months include many trying to escape gang and drug violence in their homelands. The weapon of choice used to intimidate them is often an American-made gun.

The flow of drugs and immigrants into the U.S. has been well-documented for decades and become a regular part of the political debate. But weapons smuggling from border states gets less attention.

A 2013 report by the University of San Diego says the number of firearms smuggled from the U.S. was so significant that nearly half of American gun dealers rely on that business to stay afloat.

On average, an estimated 253,000 firearms each year are purchased in the U.S. expressly to be sent to Mexico.