The topic discusses martial law, a rarely used legal concept in the United States. It explains that while not explicitly defined in law, martial law allows the military to assume control over civilian government during emergencies. The article provides historical examples of martial law's implementation in the U.S., including instances during wartime, natural disasters, and labor disputes. These examples highlight the wide range of circumstances under which martial law has been employed, from President Lincoln's use during the Civil War to a governor's declaration in Colorado. Finally, the text contrasts martial law with the Insurrection Act, clarifying that the latter involves military assistance to civilian authorities, not a complete governmental takeover.