The Insurrection Act of 1807 is the U.S. federal law that empowers the president of the United States to nationally deploy the U.S. military and to federalize the National Guard units of the individual states in specific circumstances, such as the suppression of civil disorder, of insurrection, and of armed rebellion against the federal government of the U.S.[1] The Insurrection Act provides a statutory exception to the Posse Comitatus Act (1878) that limits the president's deploying the U.S. military to enforce either civil law or criminal law within the United States.[2][3].
After invoking and before exercising the powers authorized under the Insurrection Act, Title 10 U.S.C. § 254 requires the publication of a presidential proclamation whereby the U.S. President formally orders the dispersion of the peoples committing civil unrest or armed rebellion. The Defense Department guidelines define "homeland defense" as a constitutional exception to the restrictions of the Posse Comitatus Act, therefore, the political, military, and police measures necessary to protect national security from external threats are exceptions to the restrictions of the act.[2][3]