What is the Alien Enemies Act? Here’s how the 1798 law was invoked in the past.

The Alien Enemies Act, established in 1798, was designed to give the president of the United States more power over foreign nationals on American soil during times of war. This month, Donald Trump invoked the law in an executive order targeting the Venezuelan gang Tren de Aragua, which the White House says is conducting “irregular warfare” against the U.S. The administration subsequently deported more than 200 men—who may or may not have ties to the gang—to a Salvadoran prison before a judge temporarily blocked the removals. (The administration is appealing the ban, but the men remain in El Salvador while their legal status is challenged.)

The White House claims implementing the law is necessary to ensure public safety, while others argue the longstanding statute should not be used since the U.S. is not in a declared war with Venezuela. In a memorandum blocking the removals, federal judge James E. Boasberg acknowledged that the executive’s use of the Alien Enemies Act raises “thorny legal issues” that “loom on the horizon,” calling Trump’s use of the law “unprecedented.”

Here’s what to know about the law and how it’s been used against non-citizens throughout American history.

The history behind the Alien Enemies Act

The Alien Enemies Act was one of four 1798 laws known as the Alien and Sedition Acts—a set of controversial statutes that emerged during a tenuous moment in the fledgling nation’s history.

In the wake of the Revolutionary War, the U.S. attempted to claim neutrality on the world stage. Yet it still faced a military threat from Great Britain, which was seizing American ships to use in its ongoing war with France. In 1794, the U.S. signed a treaty with Britain to stop the seizures and improve Anglo-American relations, but the treaty strained the American alliance with revolutionary France.

Back at home, American lawmakers were split on which nation to support. Members of the emerging Democratic-Republican party, led by Thomas Jefferson, wanted the U.S. to ally with France, while Federalists, led by John Adams and Alexander Hamilton, thought the U.S. should align itself with Great Britain. Meanwhile, French privateers began seizing American merchant vessels in retaliation. An attempt to resolve the dispute through diplomatic means backfired when French diplomats demanded bribes.

News of failed negotiations, corrupt diplomats, and ongoing French seizures of American merchant ships pushed the nation to the brink of war against France. The Federalists, who controlled Congress, feared Democratic-Republicans’ French sympathies—and looked with suspicion on non-citizen residents they thought of as “aliens.” Unlike those who arrived before them, these new immigrants were largely poor and had not been in America during the Revolution or at the time of the country’s founding, leading to debates on their ability to self-govern and their potential political leanings. Federalists worried that these immigrants would join the opposition party once they became citizens—and that they would lend their support to France if the nations went to war.

Those fears spurred the Federalist Congress to pass the Alien and Sedition Acts, slow down the citizenship process, and give the president authority to exert control over non-citizen residents during wartime. The Sedition Act criminalized anti-government speech, while the Naturalization Act increased the residency requirement for potential citizens from five to 14 years. The Alien Friends Act allowed the president to deport any non-citizen considered dangerous, and the Alien Enemies Act gave the president special authority to deem entire swaths of non-citizens dangerous and restrict their civil liberties during wartime.

In response to the passing of these acts, James Madison and Thomas Jefferson drafted the Virginia and Kentucky resolutions, respectively, arguing that the laws were unconstitutional and that states had the right to prevent them from being invoked within their borders. However, these resolutions were rejected by the 14 other states of the new republic, and the laws stood despite their unpopularity.

Three of the laws lived only as long as the undeclared conflict with France, now known as the Quasi-War. After the Alien Friends and Sedition Acts expired in 1801, they were not renewed, and a new 1802 naturalization law reduced the residency period of the older act. But the Alien Enemies Act is still in effect today.

What powers does the Alien Enemies Act grant the president?

The law covers any “natives, citizens, denizens, or subjects” of a hostile government who live in the U.S. and are age 14 or older. Though the Act at first only included males, this restriction was removed during a World War I-era amendment designed to expand the law’s reach to female non-citizens.

The act gives the president sweeping powers to decide on national policy toward non-citizens during wartime, requiring only that the executive proclaim the war, invasion, or threat before using the law. In effect, it gives the president power to apprehend, imprison, and deport “alien enemies,” potentially bypassing due process during wartime—and allows the president to decide “the manner and degree” of the way in which they are apprehended and held before deportation.

How has the Alien Enemies Act been used before?

Since France and the U.S. never declared war in 1798, the Alien Enemies Act was not invoked during the conflict that birthed it. But it has been used three other times in history: during the War of 1812 and World Wars I and II.

In the midst of the War of 1812, President James Madison declared British citizens enemy aliens. At this time, British citizens under those restrictions had to report to state authorities, were forced to move away from coastal areas, and faced travel restrictions and ongoing monitoring, but it’s unclear how many were forced to move, detained, or deported under the law.

More than a century later, the law was again invoked during World War I. After Congress proclaimed war in 1917, President Woodrow Wilson made a proclamation declaring male German citizens residing in the U.S.—and shortly after, Austro-Hungarians and female Germans—enemy aliens. This restricted their rights to firearm ownership, their ability to write or publish anything critical of the U.S., and residence near military facilities.

(Why the League of Nations was doomed before it began.)

Historians estimate that about 10,000 Germans and Austro-Hungarians were arrested in the U.S. during World War I. About 2,000 deemed particularly dangerous by federal officials were incarcerated in camps in Mississippi and Georgia. Many were held past the war’s 1918 end and into 1920.

“Enemies” within during World War II

The law’s use during World War II is by far its most infamous invocation.

After Japan’s surprise attack on Pearl Harbor in 1941, the U.S. entered the Second World War and President Franklin D. Roosevelt issued three proclamations deeming Japanese, German, and Italian non-citizens enemy aliens. Federal and local officials had already begun rounding up and interrogating Japanese Americans soon after the attack, indiscriminately arresting community leaders, many of whom were released after a brief detention. Others were held long after war was declared. Within months, thousands had been imprisoned, their personal property seized and their freedoms curtailed.

(83 years after Pearl Harbor, here’s how the attack changed history.)

The U.S. rounded up and incarcerated about 31,000 people of Japanese, German, and Italian ancestry in camps across the country throughout and even beyond the war. These arrests and detentions were often carried out with little evidence aside from nationality.

The law’s use during World War II set the stage for an even more sweeping restriction of civil liberties based on ancestry: the incarceration of about 120,000 civilians of Japanese ancestry—many American citizens. Though the Japanese American incarceration relied on other legal means, including executive and military orders, the use of the Alien Enemies Act paved the way for the detention and incarceration of large swaths of loyal residents during the war.

(The U.S. forced them into internment camps. Here’s how Japanese Americans started over.)

Should the Alien Enemies Act be revoked?

Despite its role during World War II, which Congress formally acknowledged as a “fundamental injustice” in 1987, the Alien Enemies Act remains federal law. Its legality was even upheld after World War II, when it was challenged in 1948 by a deported German national.

In Ludecke v. Watkins, the U.S. Supreme Court found that the law does not violate the Bill of Rights because a “period of confusion and conflict which is characteristic of a state of war” remained in force during the immediate postwar period. But dissenting judges raised questions about the extent to which a single elected person can override “essential liberties,” even during wartime.

Civil liberties and immigrants’ rights groups, among others, have long warned the Alien Enemies Act might be misused against non-citizens. Among them is former Representative Mike Honda (D-CA), who served in Congress between 2001 and 2017.

“It may have been written in 1798, but if it’s still on the books, it still can be used,” says Honda, who was incarcerated in a Colorado camp as a young child during World War II due to his Japanese American heritage. Honda spearheaded an attempt to have the law struck down or rewritten during the Obama administration, but his proposed legislation died in committee. Though reintroduced in later sessions of Congress, the proposed Neighbors, Not Enemies Act has yet to become law.

For now, the Alien Enemies Act remains on the books—and will doubtlessly persist as a flashpoint in ongoing debates about immigration, civil liberties, and national security.