Posse comitatus

Posse comitatus, literally the force of the county, refers to a group of civilians mobilized by law enforcement under common law principles to address emergencies and maintain public order, acting for a lawful reason and remaining under the authority of a peace officer such as a sheriff or justice. The doctrine traces to ninth-century England during the campaigns of Alfred the Great, developing out of older customs of locally organized forces. It continues to exist today in common law jurisdictions that have not repealed it by statute; in the United States, the Posse Comitatus Act of 1878 specifically restricts the use of federal military forces for domestic law enforcement without congressional approval, while the civilian posse power itself remains available to sheriffs in many states. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/