Posse Comitatus

In 1878 the use of a posse comitatus was limited by the passage of the Posse Comitatus Act of 1878. This act, passed in response to the use of federal troops to enforce reconstruction policies in the southern states, prohibited the use of the U.S. Army to enforce laws unless the Constitution or an act of Congress explicitly authorized such use. This act was amended five times in the 1980s, largely to allow for the use of military resources to combat trafficking in illicit narcotics. The Insurrection Act of 1807 provides an exception to the Posse Comitatus Act, authorizing the president to deploy both the regular U.S. military and the active-duty National Guard in cases of insurrection and rebellion.