Posse Comitatus Act

The Posse Comitatus Act of 1878 is a United States federal law that restricts the use of the U.S. military for domestic law enforcement purposes. It was enacted following the Reconstruction era to prevent the military from being used to enforce laws in the South. The Act generally prohibits the use of the military for civilian law enforcement unless expressly authorized by the Constitution or an Act of Congress.12

Historically, the term "posse comitatus" referred to a group of able-bodied citizens summoned by a sheriff to help maintain public order or pursue felons. While this ancient institution has been preserved in some U.S. states, the 1878 Act specifically addresses the federal military's role. The Insurrection Act serves as an exception, allowing for military deployment in specific circumstances when authorized by law.132