Exploring Military Involvement in Southern Border Operations and Strategy

U.S. military forces along the southern border have been granted expanded authority to detain illegal immigrants on newly designated military land, marking a significant shift in border security strategy under the Trump administration.

Quick Takes

Military personnel can now detain illegal immigrants and conduct security operations on a 60-foot-wide strip of land along the U.S.-Mexico border in New Mexico.
President Trump transferred nearly 110,000 acres from the Department of Interior to the Army on April 11 for border security operations.
The New Mexico National Defense Area spans more than 170 miles, with plans to add 90+ miles in Texas.
Over 10,000 service members are currently deployed to support Customs and Border Protection operations.
Military forces can now implement crowd control measures, assist with barrier construction, and conduct searches until law enforcement arrives.

Military Given Expanded Border Security Role

U.S. Northern Command announced that military personnel stationed along the southern border have been authorized to detain and search undocumented migrants crossing into a newly designated military zone in New Mexico. This authorization represents a substantial expansion of military involvement in immigration enforcement. The area, formally known as the New Mexico National Defense Area (NMNDA), consists of a 60-foot-wide strip of land along the U.S.-Mexico border that has been reclassified as part of Arizona’s Fort Huachuca military installation, effectively bringing it under Department of Defense jurisdiction.

The transfer occurred through President Trump’s memorandum, which moved control of the Roosevelt Reservation area from the Department of the Interior to the Department of Defense. This strategic reclassification grants military forces the authority to conduct security operations that were previously limited to civilian law enforcement agencies. In total, nearly 110,000 acres of federal land were transferred to the Army to support Border Patrol operations for a three-year period, creating a militarized zone spanning approximately 170 miles.

🇺🇸 Fox News: US military personnel in a New Mexico National Defense Area near the southern border can now temporarily detain & search illegal migrants. This shifts their role beyond traditional support, allowing detention of trespassers until law enforcement arrives. pic.twitter.com/UKLx7wA4BH

— Faytuks Network (@FaytuksNetwork) April 21, 2025

New Powers and Operations

The expanded authority grants military personnel several key powers previously reserved for law enforcement. Service members in the designated area can now detain individuals crossing illegally, conduct searches, implement crowd control measures, and assist with the installation of temporary barriers and fencing. However, the military’s role remains supportive rather than primary – detained individuals must be promptly handed over to Customs and Border Protection or other law enforcement partners for processing under immigration laws.

General Gregory Guillot, commander of U.S. Northern Command, emphasized that military personnel will conduct enhanced detection and monitoring operations within the designated defense area. Over 10,000 service members are currently deployed along the southern border to support Customs and Border Protection operations. Their mission now includes security activities that extend beyond the advisory and logistical support traditionally provided by the military at the border.

Expansion Plans and Political Context

The Trump administration has signaled that this is only the beginning of an enhanced military presence at the southern border. White House press secretary Karoline Leavitt announced plans to add more than 90 miles of military jurisdiction in Texas in the coming weeks. Additionally, the administration is advancing other border security measures, including a waiver to expedite border wall construction in southern California, bypassing environmental laws to speed up the construction of 2.5 miles of barrier outside San Diego.

Defense Secretary Pete Hegseth has been vocal about the military’s commitment to border security, stating “DoD keeps delivering for the American people. President Trump said to LOCK-DOWN the border – and we are.” The expanded military role has faced criticism from Democrats, who cite resource burdens and costs. The Defense Department’s southern border operations are estimated to cost nearly $1 billion over eight months. Meanwhile, Border Patrol has reported a significant drop in apprehensions of illegal immigrants from March 2024 to the following month, though it remains unclear how much of this decrease can be attributed to the enhanced military presence.