KEY TAKEAWAYS
- Martial law means military authorities take over functions normally run by civilian government, such as policing and courts. The Constitution never mentions it, and no federal statute defines it.
- The Supreme Court set the main limit in Ex parte Milligan (1866): civilians can’t be tried by military tribunals where the civilian courts are open and working.
- Martial law has never been declared nationwide in the United States. The longest modern example was Hawaii, from December 1941 to October 1944.
- The Insurrection Act and National Guard deployments are not martial law. They let troops support civilian authorities, which stay in charge, and the Insurrection Act was last formally invoked in 1992.
- In December 2025 the Supreme Court refused to let the administration deploy National Guard troops in Illinois under 10 U.S.C. § 12406, keeping a lower-court block in place.
- What Is Martial Law?
- Who Can Declare Martial Law?
- What the Supreme Court Has Said
- Martial Law in U.S. History
- Martial Law vs. the Insurrection Act and Guard Deployments
- Recent Events: 2025 and 2026
- Martial Law Elsewhere: South Korea, 2024
- Common Myths
- Frequently Asked Questions
Martial law is one of the most searched and least understood terms in American government. It has been declared in the United States only a handful of times, always locally, and the Supreme Court has spent 175 years narrowing what it can do. Questions about it spike whenever troops appear on American streets, as they did in 2025, and again as the 2026 midterm elections approached. This guide explains what martial law is, who can declare it, how it differs from the Insurrection Act and Guard deployments, and what history and the courts say about its limits.
What Is Martial Law?
Martial law is the temporary replacement of civilian government by military authority. Under martial law, military commanders, rather than elected officials, police and civilian judges, can control public order: enforcing curfews, detaining people, and in the most extreme form, trying civilians in military courts.
The Constitution doesn’t mention martial law, and no federal law defines it or says who may declare it. What the Constitution does contain is the Suspension Clause in Article I, Section 9, which allows the privilege of habeas corpus, the right to challenge detention in court, to be suspended “when in Cases of Rebellion or Invasion the public Safety may require it.” Because that clause sits in Article I, the legislative article, most scholars read it as a power belonging to Congress.
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Martial law is different from military law, the Uniform Code of Military Justice, which governs service members and applies all the time. Martial law is about the military exercising authority over civilians.
Who Can Declare Martial Law?
There is no clear answer, which is a large part of why the subject provokes so much argument.
- The President. No statute gives the President power to declare martial law. Arguments for such a power rest on the President’s role as commander in chief and duty to execute the laws. Most legal scholars, and the Supreme Court’s decisions below, treat any such power as narrow and subject to court review.
- Congress. Congress controls the suspension of habeas corpus and the laws governing domestic use of the military, so it can authorize or restrict military action at home.
- Governors. Many state constitutions and laws give governors emergency powers over their state’s National Guard, and governors have declared martial law locally many times, often during labor disputes and natural disasters.
Even where a declaration is made, the courts have consistently held that it doesn’t put officials beyond legal limits. That principle runs through every major case.
What the Supreme Court Has Said
Four decisions set the boundaries:
| Case | Year | What the Court held |
|---|---|---|
| Luther v. Borden | 1849 | Rhode Island could declare martial law to put down the Dorr Rebellion, and which of two rival state governments was legitimate was a political question for Congress and the President, not the courts. |
| Ex parte Milligan | 1866 | A civilian in Indiana could not be tried by a military commission while the civilian courts were open and functioning, even during the Civil War. |
| Sterling v. Constantin | 1932 | A Texas governor’s martial law declaration over the East Texas oil fields did not put his actions beyond federal court review. |
| Duncan v. Kahanamoku | 1946 | Martial law in wartime Hawaii did not authorize military tribunals to replace civilian courts for trying civilians. |
Read together, the cases say that a government can take emergency military measures, but courts will review them, and military trials of civilians are off-limits wherever civilian courts can operate. Milligan‘s line that martial rule “can never exist where the courts are open” is still the most cited sentence on the subject.
Martial Law in U.S. History
New Orleans, 1814–1815
General Andrew Jackson imposed martial law on New Orleans before and after the Battle of New Orleans. When a federal judge challenged him, Jackson had the judge removed from the city. After martial law ended, the judge fined Jackson $1,000 for contempt, a fine Congress later refunded with interest decades afterward.
The Civil War
President Lincoln suspended habeas corpus in parts of the country in 1861 without waiting for Congress, and Chief Justice Roger Taney, sitting as a circuit judge in Ex parte Merryman, ruled that only Congress could do so. Lincoln continued, and Congress authorized suspension in 1863. Military commissions tried civilians in several states, which led to the Milligan decision after the war.
State Declarations
Governors have declared martial law locally many times. Idaho’s governor did so during the Coeur d’Alene mining conflicts of 1892 and 1899, and Texas Governor Ross Sterling declared it over the East Texas oil fields in 1931 to enforce production limits, which led to Sterling v. Constantin. Declarations during strikes and disasters were relatively common in the early 20th century and have been rare since.
Hawaii, 1941–1944
Hours after the attack on Pearl Harbor on December 7, 1941, Hawaii’s territorial governor declared martial law with President Roosevelt’s approval. The military ran the territory for nearly three years, controlling courts, curfews, wages and the press, until martial law ended in October 1944. It remains the longest and most sweeping use of martial law in modern U.S. history, and the Supreme Court later ruled in Duncan v. Kahanamoku that the military trials of civilians held under it were unlawful.
No President has declared martial law across the whole country.
Martial Law vs. the Insurrection Act and Guard Deployments
Most of what gets called “martial law” in the news is one of these instead. The difference is who is in charge: in each case below, civilian government stays in control and troops support it.
| Authority | What it does | Who’s in charge |
|---|---|---|
| Insurrection Act (10 U.S.C. §§ 251–255) | Lets the President use active-duty troops or federalized Guard to suppress insurrection or enforce federal law when normal enforcement fails | Civilian government; courts stay open |
| 10 U.S.C. § 12406 | Lets the President call state Guard into federal service for invasion, rebellion, or when federal law can’t be executed with the regular forces | Civilian government |
| State active duty / Title 32 | Governor uses the state’s National Guard, paid by the state or federal government, for emergencies and disasters | Governor |
| Posse Comitatus Act (18 U.S.C. § 1385) | Makes it a crime to use the Army, Navy, Marine Corps, Air Force or Space Force to enforce civilian law unless the Constitution or Congress expressly allows it | Restricts federal troops |
| Martial law | Military authority replaces civilian authority | Military commanders |
The Insurrection Act is the main legal exception to the Posse Comitatus Act. Presidents have invoked it more than two dozen times, including to enforce school desegregation in the 1950s and 1960s, and most recently in 1992, when President George H.W. Bush used it during the Los Angeles riots. Even then, civilian courts kept operating.
National Guard members serving under a governor’s command are not covered by the Posse Comitatus Act, which is why governors can use them for law enforcement support in ways federal troops can’t. Our guide to National Guard and Reserve age limits covers how the Guard’s state and federal roles work for those who serve.
Recent Events: 2025 and 2026
The question of troops on American streets moved from history to the news in 2025. The main developments, as reported through October 2026:
- June 2025, Los Angeles. President Trump federalized part of the California National Guard under § 12406 during protests over immigration enforcement. California sued in Newsom v. Trump. In September 2025 a federal judge ruled the deployment violated the Posse Comitatus Act; appeals followed, and the troops were ordered out of the city in December 2025.
- August 2025 onward, Washington, D.C. The President, who commands the D.C. National Guard directly because D.C. is a federal district, activated it under an emergency order, joined by Guard units from several states. An Army memo reported in January 2026 extended the mission through the end of 2026.
- December 2025, the Supreme Court. In an unsigned order on December 23, 2025, the Court refused to let the administration deploy Guard troops in Illinois, reading “regular forces” in § 12406 as likely meaning the regular military. Three justices dissented.
- December 31, 2025. The President ended the Guard deployments in Los Angeles, Chicago and Portland.
- January 2026, Minnesota. The President threatened to invoke the Insurrection Act during protests over immigration enforcement but did not do so.
In the weeks before the November 2026 midterm elections, talk of martial law resurfaced after a lawyer on a September 30 online call with election activists said it might be needed in the event of a “rigged” election. As Newsweek reported, the White House did not say whether the President would consider it, and legal experts noted that no statute gives a President martial law power. Federal law also makes it a crime for federal officers to bring troops to a polling place, except to repel armed enemies of the United States, under 18 U.S.C. § 592.
None of the 2025 or 2026 deployments was a declaration of martial law: civilian governments and courts kept operating, and the courts reviewed the deployments as they happened.
Martial Law Elsewhere: South Korea, 2024
Much of the recent search interest came from abroad. On December 3, 2024, South Korean President Yoon Suk Yeol declared martial law; the National Assembly voted to lift it within hours, and Yoon was impeached and later removed from office in 2025. The episode showed how quickly a legislature and courts can reverse a declaration when they keep functioning.
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Common Myths
- “The President can declare martial law at any time.” No statute grants that power, and the Supreme Court has repeatedly limited emergency military rule.
- “Sending in the National Guard means martial law.” Guard deployments under a governor, Title 32 or § 12406 leave civilian authorities in charge.
- “The Insurrection Act is martial law.” It allows troops to support law enforcement, but civilian government and courts remain in place.
- “Martial law suspends the Constitution.” Courts have held that constitutional limits continue to apply, and Milligan bars military trials of civilians where courts are open.
For more on how military service intersects with civilian life, see our guides to the Selective Service System and how the military draft works.
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Frequently Asked Questions
No. Martial law has only ever been declared locally in the United States, by military commanders in specific places such as New Orleans in 1814 and Hawaii during World War II, or by governors within their own states. No President has declared nationwide martial law.
No federal law gives the President that power, and the Constitution doesn’t mention martial law. Arguments for a presidential power rely on the commander-in-chief role, but the Supreme Court has repeatedly limited military rule over civilians, most importantly in Ex parte Milligan (1866), which held that civilians can’t be tried by military courts where civilian courts are open.
No. The Insurrection Act lets the President use troops to suppress insurrection or enforce federal law when normal enforcement fails, but civilian government and the courts remain in charge. It was most recently invoked in 1992 during the Los Angeles riots. Martial law, by contrast, replaces civilian authority with military authority.
Many state constitutions and laws give governors emergency powers over their National Guard, and governors have declared martial law locally in the past, during strikes, riots and disasters. Those declarations are still subject to court review: in Sterling v. Constantin (1932), the Supreme Court held that a Texas governor’s martial law order couldn’t override federal court authority.
Federal law prohibits it. Under 18 U.S.C. § 592, it is a crime for a federal civil, military or naval officer to bring or keep troops at a polling place, unless the force is needed to repel armed enemies of the United States. A related law, 18 U.S.C. § 593, bars military interference with elections.
No. The D.C. National Guard answers to the President because D.C. is a federal district, not a state, and Guard troops there have supported civilian law enforcement rather than replacing it. Civilian police, the D.C. government and the courts continued to operate throughout the deployment.
This article is provided by USMilitary.org, an independent educational resource. We are not affiliated with the Department of Defense, the National Guard Bureau, any political party or campaign, or any government agency, and this article does not take a position on any current political dispute. It is general information, not legal advice; recent events are summarized as reported through October 22, 2026.
