The Posse Comitatus Act of 1878

National Guard members patrol New Orleans.
National Guard members patrol New Orleans following Hurricane Katrina. Ethan Miller / Getty Images

"Posse Comitatus" translates to "force of the country." In its purest form, posse comitatus is an ancient English doctrine that allowed law enforcement agents to recruit able-bodied men in times of strife, effectively deputizing them to help keep the peace. The American colonies made ample use of the concept, as did towns in the expanding Western frontier. The practice gave birth to the more common term, "posse." 

The Posse Comitatus Act of 1878

The Posse Comitatus Act of 1878 was passed to prevent US military personnel from acting as law enforcement agents on US soil. This was common practice before 1878, particularly in areas of the West where the US military was often the only law enforcement to be found. Soldiers often enforced civilian laws whenever it was necessary.

The Posse Comitatus Act banned this practice, and the Act still remains in effect. The text (18 U.S.C. Section 1385), reads:

"Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both."

Unintended Consequences 

While the Act is seen as an essential element of the American civil liberties framework, it originally represented a profound betrayal of African-American Southerners by the federal government.

US troops were stationed in the South to protect recently freed black slaves in the Reconstruction years following the American Civil War. This protection allowed black Southerners to vote and sought to ensure that they could function as free people.

The Posse Comitatus Act withdrew US troops from Southern soil.

When lawmakers agreed to end Reconstruction in exchange for electoral votes during the controversial 1876 presidential election, black Southerners were subjected to nearly a century of Jim Crow laws—those that legalized segregation—with almost no federal protection. 

The Posse Comitatus Act Today 

The Posse Comitatus Act has taken on a very different meaning from that which was intended in 1878. No longer associated with Reconstruction, the Act provides a useful way to prevent the US armed forces from directing their efforts against US dissident groups. Public sentiment in favor of the Posse Comitatus Act is strong. A 2006 law was enacted in response to Hurricane Katrina that permitted an exception to the Act in cases of public disasters, but it was repealed a year later.

Technically, the Act applies only to the US Army and the Air Force. The Coast Guard is considered law enforcement, and the Coast Guard does not report to the Department of Defense; therefore, it is exempt. The Act can be overridden by the president in cases of extreme emergencies. It effectively bars local law enforcement from calling up the militia for help enforcing state laws, although state governors may request the assistance of the National Guard under some circumstances.


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Head, Tom. "The Posse Comitatus Act of 1878." ThoughtCo, Nov. 1, 2017, Head, Tom. (2017, November 1). The Posse Comitatus Act of 1878. Retrieved from Head, Tom. "The Posse Comitatus Act of 1878." ThoughtCo. (accessed April 20, 2018).