The exercise of government and control by military authorities over the civilian population of a designated territory.
Martial law is an extreme and rare measure used to control society during war or periods of civil unrest or chaos. According to the Supreme Court, the term martial law carries no precise meaning (Duncan v. Kahanamoku, 327 U.S. 304, 66 S. Ct. 606, 90 L. Ed. 688 ). However, most declarations of martial law have some common features. Generally, the institution of martial law contemplates some use of military force. To a varying extent, depending on the martial law order, government military personnel have the authority to make and enforce civil and criminal laws. Certain civil liberties may be suspended, such as the right to be free from unreasonable searches and seizures, freedom of association, and freedom of movement. And the writ of Habeas Corpus may be suspended (this writ allows persons who are unlawfully imprisoned to gain freedom through a court proceeding).
In the United States, martial law has been instituted on the national level only once, during the Civil War, and on a regional level only once, during World War II. Otherwise, it has been limited to the states. Uprisings, political protests, labor strikes, and riots have, at various times, caused several state governors to declare some measure of martial law.
Martial law on the national level may be declared by Congress or the president. Under Article I, Section 8, Clause 15, of the Constitution, Congress has the power "[t]o provide for calling forth the Militia to execute the Laws of the Union, suppress insurrections and repel Invasions." Article II, Section 2, Clause 1, of the Constitution declares that "[t]he President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States." Neither constitutional provision includes a direct reference to martial law. However, the Supreme Court has interpreted both to allow the declaration of martial law by the president or Congress. On the state level, a governor may declare martial law within her or his own state. The power to do so usually is granted in the state constitution.