Question: When was the last time martial law was established in the USA?

Martial law in the United States

Martial law in the United States refers to several periods in United States history wherein a region or the United States as whole are placed under the control of a military body. On a federal level, only the president has the power to impose Martial Law. In each state the governor has the right to impose martial law within the borders of the state. In the United States, martial law has been used in a limited number of circumstances, such as directly after a foreign attack, such as Hawaii after the Japanese attack on Pearl Harbor or New Orleans during the Battle of New Orleans; after major disasters, such as the Great Chicago Fire of 1871 or the San Francisco earthquake of 1906; local leaders declared martial law to protect themselves from mob violence, such as Nauvoo, Illinois, during the Illinois Mormon War, or Utah during the Utah War; or in response to chaos associated with protests and mob action, such as the 1934 West Coast waterfront strike, or mob actions against the Freedom Riders.  
The martial law concept in the United States is closely tied with the right 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 related to the imposition of martial law.[1] Article 1, Section 9 of the US 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."  There have been many instances of the use of the military within the borders of the United States, such as during the Whiskey Rebellion and in the South during the Civil Rights Movement, but these acts are not tantamount to a declaration of martial law. The distinction must be made as clear as that between martial law and military justice: deployment of troops does not necessarily mean that the civil courts cannot function, and that is one of the keys, as the Supreme Court noted, to martial law.
In 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 1878, Congress passed the Posse Comitatus Act, which forbids military involvement in domestic law enforcement without congressional approval.
Throughout United States history are several examples of the imposition of martial law, aside from that during the Civil War.
The American Revolution

As a result of the Boston Tea Party, Parliament passed the Massachusetts Government Act, one of the Intolerable Acts, which suppressed town meetings and assemblies, and imposed appointed government, tantamount to martial law.[2][3][4]
New Orleans, Louisiana in the War of 1812
During the War of 1812, US General Andrew Jackson imposed martial law in New Orleans, Louisiana, before repulsing the British in the Battle of New Orleans.[5][6][7] Martial law was also imposed in a four-mile radius around the vicinity. When word came of the end of the war, Jackson maintained martial law, contending that he had not gotten official word of the peace. A judge demanded habeas corpus for a man arrested for sedition. Rather than comply with the writ, Jackson had the judge arrested.
Nauvoo, Illinois, during the Illinois Mormon War
In 1843, Missouri sought to extradite Joseph Smith, the founder of Mormonism, for the attempted murder of Missouri governor Lilburn Boggs. He escaped arrest with the help of members of his church, and was discharged on a writ of habeas corpus in the Municipal Court of Nauvoo, where he was mayor, even though it was outside the court's jurisdiction. People in the neighboring town of Carthage, Illinois, felt that Smith was abusing his position in order to avoid arrest. They requested that Governor Ford call out the militia to take Smith into custody, to which Governor Ford declined.[8]:139 A group of ex-Mormons published a paper called the Nauvoo Expositor which detailed Smith's alleged abuse of power. Together with the Nauvoo City Council, Smith ordered the destruction of the Nauvoo Expositor. This caused an uproar in neighboring towns, who interpreted the order as an attack on the freedom of speech. Smith was charged with causing a riot, which the Nauvoo courts dismissed.  Neighboring cities raised money for a militia to go and capture Smith.[9] Governor Ford arrived in Carthage and sent word to Smith that if he did not surrender, Ford would call out the militia. On June 18, Smith declared martial law[10] in Nauvoo and called out the Nauvoo Legion, an organized city militia of about 5,000 men,[11] to protect Nauvoo from outside violence.[10]  Ford sent a group of men and abolished martial law. By this time, Smith had escaped into Iowa, but was convinced by his supporters to return. He was arrested for treason against the state of Illinois for declaring martial law.[9]  While awaiting trial in Carthage Jail, Smith was murdered by a mob.  In 1845, Nauvoo was stripped of its charter for abuse of authority. This led to a series of conflicts known as the Illinois Mormon War.[12]
Utah during the Utah War

Tension between Utah territory and the federal government was strained in 1857 due to the influence of theodemocracy in the Governor Brigham Young's semi-theocratic government, Utah's rejection of Federal appointees, and Utah's acceptance of polygamy and slavery. In 1857, President James Buchanan sent U.S. forces to the Utah Territory in what became known as the Utah War. The Mormons, fearful that the large U.S. military force had been sent to annihilate them, made preparations for defense. On 15 September, Young publicly declared martial law in Utah. It was widely circulated throughout the Territory and was delivered by messenger to Col. Alexander with the approaching army. The most important provision forbade "all armed forces of every description from coming into this Territory, under any pretense whatsoever."[13] It also commanded that "all the forces in said Territory hold themselves in readiness to march at a moment's notice to repel any and all such invasion."[13] But more important to California and Oregon bound travelers was the third section that stated "Martial law is hereby declared to exist in this Territory...and no person shall be allowed to pass or repass into, through or from this territory without a permit from the proper officer."[13] Brigham Young ordered the people in Salt Lake City, Utah to burn their homes and retreat south to Provo, Utah. Meanwhile, the Mormons harassed the approaching army. Eventually, Brigham Young was removed as governor and replaced by Alfred Cumming.
Ex parte Milligan
On September 15, 1863, President Lincoln imposed Congressionally authorized martial law.[14] The authorizing act allowed the President to suspend habeas corpus throughout the entire United States (which he had already done under his own authority on April 27, 1861). Lincoln imposed the suspension on "prisoners of war, spies, or aiders and abettors of the enemy," as well as on other classes of people, such as draft dodgers. The President's proclamation was challenged in Ex parte Milligan, 71 US 2 [1866]. The Supreme Court ruled that Lincoln's imposition of martial law (by way of suspension of habeas corpus) was unconstitutional in areas where the local courts were still in session.
The Great Chicago Fire

In response to the Great Chicago Fire of 1871, Chicago mayor Roswell B. Mason declared a state of martial law and placed General Philip Sheridan in charge of the city on October 9, 1871. After the fire was extinguished, there were no widespread disturbances and martial law was lifted within a few days.[15]
Coeur d'Alene, Idaho, 1892
In 1892, in Coeur d'Alene, Idaho, striking mine workers blew up a mill and shot at strike-breaking workers. The explosion leveled a four-story building and killed one person. The governor declared martial law. At the same time, a request was made for federal troops to back guardsmen. Over 600 people were arrested. The list was whittled down to two dozen ringleaders who were tried in military court. While in prison, the mine workers formed a new union, the Western Federation of Miners.
San Francisco earthquake of 1906
Following the earthquake of 1906, the troops stationed in the Presidio were pressed into martial law service. Guards were posted throughout the city, and all dynamite was confiscated. The dynamite was used to destroy buildings in the path of fires, to prevent the fires from spreading.
Colorado Coalfield War
In 1914, imposition of martial law climaxed the so-called Colorado Coalfield War. Dating back decades, the conflicts came to a head in Ludlow, Colorado in 1913. The Colorado National Guard was called in to quell the strikers. For a time, the peace was kept, but it is reported that the make-up of the Guard stationed at the mines began to shift from impartial normal troops to companies of loyal mine guards. Clashes increased and the proclamation of martial law was made by the governor, eventually resulting in the Ludlow Massacre. President Wilson sent in federal troops, eventually ending the violence.
On August 19, 1917, the Spokane office of the IWW (Industrial Workers of the World, or Wobblies) was raided, leaders arrested, and martial law was declared. The military authority was the National Guard, controlled by the U.S. War Department. This occurred in reaction to a demand by IWW leader James Rowan that all prisoners of the "class war" (he meant Wobbly strikers and strike leaders involved in a statewide lumber strike) be released or Spokane would face a general strike. 
The repression of the democratic, radical union in Spokane and across the state took place in the context of the Wobbly-led loggers'and sawmill workers'ongoing strike for the eight-hour day and sanitary conditions in the camps. The IWW was militant, radical, vocal and consistently nonviolent. 
The larger context of the repression of the union was war hysteria, combined with employer opposition to union demands. The nationwide suppression of the IWW during the war involved physical violence, vandalism, and the imprisonment of hundreds of union members and leaders.
West Virginia Coal Wars
During the events of the West Virginia Coal Wars (1920–1921), martial law was declared in the state of West Virginia. At the behest of Governor Cornwell, federal troops had been dispatched to Mingo County to deal with the striking miners. The army officer in charge acted, ostensibly, under the Suspension Clause of Article I of the United States Constitution (selectively; accounts show that he only jailed union miners), and did not allow assembly of any kind. If his soldiers found any union miners, they immediately took them and imprisoned them. The jails filled up so quickly that he had to release miners. As it went, miners were arrested, jailed, and released without any sort of trial. After a time, when the trial of Sid Hatfield began, the military occupation and "veritable military dictatorship" (Governor Cornwell) of the army officer ended. Many of the miners were not released from jail. It was only the first of three times that federal troops would be called to quiet the miners in the West Virginia Mine War.
San Francisco, California, 1934
In 1934, California Governor Frank Merriam placed the docks of San Francisco under martial law, citing "riots and tumult" resulting from a dock worker's strike. The Governor threatened to place the entire city under martial law. The National Guard was called in to open the docks, and a citywide institution of martial law was averted when goods began to flow. The guardsmen were empowered to make arrests and to then try detainees or turn them over to the courts.
The Territory of Hawaii

During World War II (1939 to 1945) what is now the State of Hawaii was held under martial law from December 7, 1941 to October 24, 1944, following the Japanese attack on Pearl Harbor.[16] After the war, the federal judge for the islands condemned the conduct of martial law, saying, "Gov. Poindexter declared lawfully martial law but the Army went beyond the governor and set up that which was lawful only in conquered enemy territory namely, military government which is not bound by the Constitution. And they ... threw the Constitution into the discard and set up a military dictatorship."[17]
Freedom Riders

On May 21, 1961, Governor Patterson of Alabama declared martial law "as a result of outside agitators coming into Alabama to violate our laws and customs" which had led to "outbreaks of lawlessness and mob action."[18] The agitators were Freedom Riders, peaceful civil rights activists challenging the already-illegal racial segregation in the South.


Further reading
Macomb, Alexander, Major General of the United States Army, , (New York: Harper & Brothers, 1841) 154 pages.
Macomb, Alexander, Major General of the United States Army, . (Charleston: J. Hoff, 1809), republished (New York: Lawbook Exchange, June 2007). ISBN1-58477-709-5, ISBN978-1-58477-709-0.

The Concise Oxford Dictionary of Politics. Edited by Iain McLean and Alistair McMillan, Oxford University Press, 2004.
Black's Law Dictionary: Definitions of the Terms and Phrases of American and English Jurisprudence, Ancient and Modern. Henry Campbell Black. St. Paul: West Pub. Co., 1979.