Posse Comitatus Act Restricts Federal Military from Domestic Law Enforcement

President Rutherford B. Hayes signs the Posse Comitatus Act into law on June 18, 1878, restricting the use of federal military personnel to enforce domestic law. Passed as an amendment to an army appropriations bill following the end of Reconstruction, the Act prohibits using the Army, Navy, Marine Corps, Air Force, or Space Force “as a posse comitatus or otherwise to execute the laws” except when “expressly authorized by the Constitution or Act of Congress,” with violations punishable by fine or up to two years imprisonment. While framed as a response to “abuses resulting from the extensive use of the army in civil law enforcement during the Civil War and the Reconstruction,” the Act’s practical effect is to ensure that the federal government cannot use military force to protect Black voting rights or prevent white supremacist terrorism in the South.

The timing proves decisive: the Act becomes law just one year after the Compromise of 1877 ended Reconstruction and withdrew federal troops from the South. The legislation enshrines the principle that domestic law enforcement is a state and local matter, effectively abandoning Southern Black citizens to the mercy of white supremacist state governments and paramilitary organizations like the White League and Red Shirts. The Act contains exceptions, most importantly the Insurrection Act allowing the president to deploy military forces to suppress insurrection or protect civil rights when state governments are unable or unwilling—but these exceptions require presidential initiative that will rarely materialize when white supremacist violence serves the interests of the Democratic Party and northern capital’s desire for “sectional reconciliation.”

The Act’s enforcement provisions prove entirely toothless: no one has ever been convicted for violating the Posse Comitatus Act, and only two people have ever been prosecuted—both more than 140 years ago. The law is a criminal statute with no real threat of prosecution, demonstrating that its purpose is political rather than legal—providing cover for federal abandonment of civil rights enforcement. The Coast Guard remains exempt because it has express statutory authority for law enforcement, and National Guard forces are rarely covered since they report to state governors. When Guard personnel are “federalized” they become bound by the Act, but this creates a perverse incentive for presidents to avoid federal activation when doing so would require protecting civil rights against state-sponsored violence.

The Posse Comitatus Act represents a fundamental shift in American federalism, codifying the principle that the federal government should not interfere with state and local “law enforcement”—even when those entities are systematically violating citizens’ constitutional rights. The Act will be cited repeatedly throughout the 20th century to justify federal inaction in the face of lynch mobs, voter intimidation, and state-sponsored racial violence. Its passage demonstrates how “military restraint” rhetoric can serve white supremacy: by the time the Act becomes law, the military’s role in Reconstruction has already ended, making the legislation primarily symbolic—but symbolically crucial in declaring that the federal government has no responsibility to protect Black citizens from organized terrorism. The Act’s persistence into the 21st century, with expansions in 1956, 1981, and 2021 to cover additional military branches, shows how legal infrastructure created to end Reconstruction permanently constrains federal power to protect civil rights, long after the specific historical circumstances that motivated its passage have transformed.