Ex parte Milligan is the 1866 Supreme Court decision holding that military tribunals cannot try civilians when the civilian courts are open and functioning. Decided on April 3, 1866, less than a year after the Civil War ended, the ruling drew a hard constitutional line between military authority and the rights of people who are not soldiers.1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866) It remains one of the strongest limits on government power during wartime, and it has shaped legal fights from World War II through the post-9/11 era.
The Case Behind the Ruling
Lambdin P. Milligan was an Indiana lawyer who had lived in the state for twenty years and had never served in the military.2University of Missouri-Kansas City School of Law. Ex Parte Milligan, 71 U.S. 2 (1866) During the Civil War he joined a secret organization that opposed the Union effort by hiding deserters, resisting the draft, and planning to free Confederate prisoners. An army informant reported that Milligan held the rank of “major general” within the group, later known as the Sons of Liberty, and directed its operations in northeastern Indiana.3IN.gov. Lambdin P Milligan and Dissent in the Civil War
Troops arrested Milligan at his home in Huntington, Indiana, on October 5, 1864, after commanders in Indianapolis uncovered a stash of revolvers and ammunition tied to the group. Rather than face a civilian jury, he was brought before a military commission convened by General Alvin P. Hovey. The commission convicted him of conspiracy and disloyalty and sentenced him to hang on May 19, 1865.2University of Missouri-Kansas City School of Law. Ex Parte Milligan, 71 U.S. 2 (1866)
His detention relied on the wartime suspension of habeas corpus. Congress had authorized the President to suspend the writ anywhere in the country during the rebellion through the Habeas Corpus Act of 1863.4GovInfo. 12 Stat. 755 – An Act Relating to Habeas Corpus and Regulating Judicial Proceedings in Certain Cases With the writ suspended, military commanders could hold suspected disloyal citizens without filing charges in a civilian court. Milligan petitioned the federal circuit court in Indiana on May 10, 1865. The judges disagreed on the legal questions and certified the case to the Supreme Court.
What the Supreme Court Decided
The Court ruled unanimously that Milligan’s military trial was unlawful and that he should be released. Justice David Davis wrote the majority opinion, and its core holding was direct: military commissions have no authority to try civilians in states that were not invaded and not in rebellion, where the federal courts remained open and operating normally.1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866)
Davis anchored the decision in the Fifth and Sixth Amendments. The Fifth requires a grand jury indictment for serious crimes, with an explicit exception only for members of the military. The Sixth guarantees a speedy public trial by jury. Read together, the military exception in the Fifth applies only to servicemembers, and the jury trial guarantee in the Sixth covers everyone else. Milligan was a civilian, so he was entitled to a civilian trial.1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866)
The opinion’s language is unusually strong for a Supreme Court decision. Davis wrote that the Constitution “is a law for rulers and people, equally in war and in peace, and covers with the shield of its protection all classes of men, at all times and under all circumstances.” The jury trial right, he added, “is not held by sufferance, and cannot be frittered away on any plea of state or political necessity.”1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866)
The Open Courts Doctrine
The rule the case is remembered for is now called the Open Courts Doctrine. If the civilian courts in an area are functioning and accessible, military tribunals have no business trying civilians there. The laws and usages of war, Davis wrote, “can never be applied to citizens in states which have upheld the authority of the government, and where the courts are open and their process unobstructed.”1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866)
Indiana made the point plainly. Federal authority in the state had never been overthrown. The courts had always been open to hear criminal cases. The judiciary, Davis wrote, “needed no bayonets to protect it, and required no military aid to execute its judgments.” In a place like that, no wartime necessity could justify trying a civilian by military commission.
When Martial Law Is Allowed
The Court also spelled out when martial law can legitimately exist, and the standard is demanding. Martial law cannot arise from a merely threatened invasion. The necessity must be actual and present, the invasion real, and the disruption severe enough to physically close the courts and displace civilian government. Only on the active battlefield, where no civil authority remains, does the military have any basis to step in as a substitute.1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866)
Even then, martial law lasts only as long as the emergency. The moment the courts reopen, military governance must end. Continuing it after civilian authority is restored, Davis wrote, “is a gross usurpation of power.” The Court allowed that martial law might have been lawful in Virginia, where the national government was overthrown and the courts driven out, but none of those conditions had existed in Indiana.
The Split on Congressional Power
Every justice agreed Milligan should go free. They split sharply on why. The majority under Davis held that neither the President nor Congress had the constitutional power to authorize military trials of civilians when civilian courts were available. The Bill of Rights imposed an absolute barrier that no statute could remove.1Justia U.S. Supreme Court Center. Ex parte Milligan, 71 U.S. 2 (1866)
Chief Justice Salmon P. Chase led a concurring group that reached the same result on a narrower ground. They agreed the commission was unlawful because Congress had not actually authorized it, but they argued Congress could have authorized military tribunals for civilians during a national crisis, even in peaceful areas, if it chose to invoke its war powers. Chase’s view would have left the door open for future legislation creating military commissions with congressional backing. The majority slammed it shut.
That disagreement frames a question that has resurfaced repeatedly in American law: does the Constitution itself forbid military trials of civilians in functioning jurisdictions, or is that decision left to Congress? The majority said the Constitution decides. The concurrence said Congress does. The Supreme Court has not definitively resolved the gap since.
How Later Cases Narrowed Milligan
Ex parte Quirin and Enemy Combatants
The broadest reading of Milligan would forbid military tribunals for anyone not on active duty. In 1942, the Court pulled that reading back in Ex parte Quirin, the case of eight Nazi saboteurs who landed on American soil intending to attack war infrastructure. One of them, Herbert Haupt, was a U.S. citizen. The Court upheld their trial by military commission, drawing a distinction Milligan had not needed to address. Milligan was a civilian “not a part of or associated with the armed forces of the enemy.” The saboteurs were enemy combatants who had crossed military lines out of uniform to commit acts of war, making them “unlawful belligerents” subject to military justice regardless of citizenship.5Justia U.S. Supreme Court Center. Ex Parte Quirin, 317 U.S. 1 (1942) After Quirin, Milligan‘s protection applies specifically to nonbelligerents, not to all civilians in every situation.
Hamdi and Boumediene
The case returned to center stage after September 11, 2001. In Hamdi v. Rumsfeld (2004), the Court considered whether the government could hold an American citizen captured on a battlefield in Afghanistan without charging him in civilian court. The plurality distinguished Milligan on the ground that he had been a civilian arrested at home in Indiana, not a prisoner of war. Had Milligan been captured carrying a rifle on a Confederate battlefield, the plurality suggested, “the holding of the Court might well have been different.”6Legal Information Institute. Hamdi v. Rumsfeld
Four years later, in Boumediene v. Bush (2008), the Court addressed the habeas rights of Guantánamo Bay detainees and cited Milligan for the proposition that civilian courts and the military have always functioned side by side in the American system, with martial rule justified only when actual warfare makes it impossible for civilian courts to operate.7Justia U.S. Supreme Court Center. Boumediene v. Bush, 553 U.S. 723 (2008) The core insight held. The Quirin exception stayed in place.
Why the Ruling Still Matters
The pattern across a century and a half is consistent. Every major national security crisis produces pressure to bypass civilian courts, and each time, Milligan‘s framework shapes the boundaries of what the government can do. Where civilian courts are open, military tribunals cannot try civilians. Quirin carved out an exception for people who act as enemy combatants, and post-9/11 cases refined that category, but the underlying principle has never been overruled.
The unresolved question from 1866 is still unresolved. Congress has asserted authority to create military commissions, most notably through the Military Commissions Acts of 2006 and 2009. Whether those statutes could constitutionally reach civilians arrested on American soil where federal courts are open is a question the Supreme Court has not answered since Davis and Chase disagreed about it. The five-justice majority said no. The four-justice concurrence said maybe. That gap remains open.