AP Explains: Militias have patrolled US border for decades

ALBUQUERQUE, N.M. (AP) — An armed group in New Mexico whose leader faces federal firearms possession charges drew national attention last month for detaining asylum-seeking Central American families near the U.S.-Mexico border.

It's not the first time an armed militia patrolled the border amid immigration and racial tensions. Throughout U.S. history, private, armed groups have been hired or appointed themselves to police the U.S-Mexico border for a variety of reasons — from preventing black slaves from fleeing to stopping Chinese immigrants from crossing over illegally.

A look at the history of armed groups patrolling the border:

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SLAVE PATROLS

After the Mexican-American War, slave-hunting groups began monitoring the border between Texas and Mexico and watching for black slaves who had run away.

Slavery had been abolished in Mexico, and slaves from as far as Alabama sought to escape to Mexico through the southern Underground Railroad before the U.S. Civil War.

Historians say the armed horsemen sometimes went into Mexico illegally to try to capture runaway slaves but were met with resistance from the Mexican government and people. Mexico refused to return the slaves who fled there.

University of Texas doctoral candidate Maria Esther Hammack has documented how Mexican Americans helped runaway slaves avoid the patrols and escape to Mexico in the mid-1800s.

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THE TEXAS RANGERS

The Texas Rangers were recommissioned after the U.S. Civil War. Although the group was known for fighting Native American tribes and alleged bandits, historians say it also functioned as a private militia on behalf of wealthy landowners and ranchers concerned about cattle and horse thefts.

During the early 1900s, the Texas Rangers operated with impunity along the Texas-Mexico border on the...