The Posse Comitatus Act is a United States federal law enacted in 1878 that limits the powers of the federal government to use military forces for domestic law enforcement. It primarily restricts the use of the U.S. Army and U.S. Air Force in civilian law enforcement activities, ensuring that military personnel do not act as police officers on American soil. Exceptions to this law exist, allowing military involvement in certain situations, such as during natural disasters or when specifically authorized by Congress. The act aims to maintain a clear separation between military and civilian authorities, promoting the principle of civilian control over the military.