The sudden decision by South Korean President Yoon Suk Yeol to declare martial law on Tuesday made international news, bringing new attention to a controversial legal topic with a long history in the United States.
Though it's not well defined in U.S. law, martial law could be declared in the U.S., and has been imposed relatively rarely in the country's history during times of war, unrest and natural disaster.
While the specifics vary in different countries and localities, martial law generally allows for the military to control civilians temporarily during times of emergency. During these times, people's ordinary rights may be restricted.
Here's what to know about martial law in the U.S.:
Martial law is not defined in the Constitution or in any law passed by Congress, according to the Brennan Center for Justice. Rather, it is a legal theory that usually refers to when "the military has taken the place of the civilian government," the Brennan Center said, not just times when military is deployed to assist civilian authorities, such as during response to a natural disaster.
States and the federal government have imposed martial law 68 times in the nation's history, according to the Brennan Center. But such a declaration at the federal level hasn't been made since the 1940s.
"It's really an alien concept" in the U.S., William Banks, a Syracuse University College of Law Board of Advisors Distinguished Professor, previously told USA TODAY.
The president can also invoke the Insurrection Act, a law that allows the president to deploy the military specifically to curb rebellion. The Insurrection Act is not the same thing as martial law, because it typically involves military assisting law enforcement, not replacing them.
Martial law has been imposed in the U.S. during times of war, natural disaster and unrest. It has been more common at the state level than the federal level, and has included varying levels of military authority, according to the Brennan Center.
In 1814, then Gen. Andrew Jackson declared martial law in New Orleans, the first such declaration in U.S. history. At the time, Jackson was preparing for an invasion of the British army, but continued martial law for months even after winning the Battle of New Orleans. During that time, a senator was arrested after penning an opinion opposing the ongoing martial law in a newspaper. When a judge demanded the senator be either formally charged with a crime or released, Jackson ordered the judge also jailed and later banished him from the city.
During the Civil War, President Abraham Lincoln invoked martial law more than once, including in Kentucky in 1864, which lasted over a year.
One Colorado governor, James Peabody, declared martial law in several counties during the so-called Colorado labor wars between 1902 and 1904.
Hawaii was under martial law for three years after the attack on Pearl Harbor. Beginning in 1941 in the then-territory, courts were replaced by military tribunals, strict curfews were enforced and people were even banned from photographing coastal areas. It was the last time martial law was declared at the federal level.