text: United States of America\nThe martial law concept in the U.S. is closely tied with the Writ of habeas corpus, which is in essence the right to a hearing on lawful imprisonment, or more broadly, the supervision of law enforcement by the judiciary. The ability to suspend habeas corpus is often equated with martial law. Article 1, Section 9 of the U.S. Constitution states, "The privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it."\n\nIn United States law, martial law is limited by several court decisions that were handed down between the American Civil War and World War II. In Ex Parte Milligan 71 US 2 1866, the Supreme Court of the United States held that martial law could not be instituted within the United States when its civilian courts are in operation. In 1878, Congress passed the Posse Comitatus Act, which forbids military involvement in domestic law enforcement without congressional approval. The National Guard is an exception, since unless federalized, they are under the control of state governors. [5]