South Korean President Yoon Suk Yeol’s sudden decision to declare martial law on Tuesday made international headlines and brought new attention to a controversial legal issue with a long history in the United States.

Although not clearly defined in U.S. law, martial law could be imposed in the United States and has been imposed relatively rarely in the country’s history during times of war, civil unrest, and natural disasters.

While the specifics vary in different countries and locations, the laws of war generally allow the military to temporarily control civilians during emergencies. During these times, people’s general rights may be limited.

UPDATES: The South Korean president relents after declaring martial law

Here’s what you should know about martial law in the US:

How does martial law work in the USA?

According to the Brennan Center for Justice, martial law is not defined in the Constitution or in any law passed by Congress. Rather, it is a legal theory that typically refers to when “the military has taken the place of the civilian government,” according to the Brennan Center, and not just to times when the military is used to support civilian authorities , for example when responding to a natural disaster.

According to the Brennan Center, states and the federal government have declared martial law 68 times in the country’s history. But there hasn’t been such a declaration at the federal level since the 1940s.

“It’s really a foreign concept” in the United States, William Banks, a distinguished professor on the Board of Advisors at Syracuse University College of Law, previously told USA TODAY.

The president can also invoke the Insurrection Act, a law that allows the president to specifically use the military to contain rebellions. Insurrectionary law is not the same as martial law because it typically involves the military assisting law enforcement rather than substituting for it.

When was martial law declared in the USA?

Martial law was declared in the United States during times of war, natural disasters, and unrest. According to the Brennan Center, it occurred more frequently at the state level than at the federal level and involved different levels of military authority.

In 1814, then-General Andrew Jackson declared martial law in New Orleans, the first such declaration in U.S. history. At this time, Jackson was preparing for an invasion by the British Army, but maintained martial law for months after the victory at the Battle of New Orleans. During this time, a senator was arrested after writing a statement in a newspaper against ongoing martial law. When a judge demanded that the senator either be formally charged with a crime or released, Jackson ordered the judge also imprisoned and later banished him from the city.

During the Civil War, President Abraham Lincoln declared martial law more than once, including in Kentucky in 1864, which lasted over a year.

A Colorado governor, James Peabody, declared martial law in several counties during the so-called Colorado Labor Wars between 1902 and 1904.

After the attack on Pearl Harbor, Hawaii was under martial law for three years. Beginning in 1941, courts were replaced by military tribunals in the territory at the time, strict curfews were imposed, and people were even banned from taking photographs of coastal areas. It was the last time martial law was declared at the federal level.

This article originally appeared on USA TODAY: Martial law in South Korea: Could it ever happen in the US?