The U.S. Department of Defense is expanding its militarized presence along the southern Texas border, authorizing troops to detain individuals for possible federal prosecution under trespassing laws within a newly designated national defense area.
On Monday, the Air Force announced it had annexed a 250-mile (400-kilometer) stretch of the border along the Rio Grande, covering two counties and reaching cities like Brownsville and McAllen. This expansion builds on a broader military buildup launched under President Trump’s national emergency declaration.
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The area will now operate as an extension of Joint Base San Antonio, with the Air Force prepared to install warning signs immediately to mark the restricted zone.
This move follows similar designations along 170 miles in New Mexico (April) and a western Texas swath (May). The military’s role includes “enhanced detection and monitoring” and the temporary detention of trespassers, who are then transferred to law enforcement agencies.
The expansion has raised concerns among hunters, hikers, and humanitarian aid groups, who fear they may lose access to these regions.
According to the Air Force, at least three individuals have already been detained by troops in New Mexico and handed over to Border Patrol. Over 1,400 immigrants have been charged with trespassing in national defense areas—a criminal misdemeanor carrying up to 18 months in prison. Legal challenges have produced mixed rulings in court.
This militarized zone reflects the administration’s broader immigration enforcement efforts, which also include the deployment of 4,000 National Guard troops and 700 Marines to Los Angeles in response to immigration protests.
These actions are pushing the boundaries of the Posse Comitatus Act, which limits the military’s ability to perform civilian law enforcement functions.
Meanwhile, illegal border crossings have dropped sharply in 2025.
