Alien Enemies Act: 2025 Tren de Aragua Invocation and Court Review

The Alien Enemies Act is a 1798 wartime statute, now codified at 50 U.S.C. § 21, that lets the President detain, restrict, and remove non-citizens who are tied to a foreign nation the United States is at war with, or one that is invading or threatening to invade U.S. territory.¹ It supplied the legal footing for detaining more than 31,000 Japanese, German, and Italian nationals during World War II, and it remains in force. In March 2025, President Trump invoked it for the first time outside a declared war, targeting alleged members of the Venezuelan gang Tren de Aragua.²

Who the Law Reaches

The statute defines an alien enemy narrowly and functionally. Under 50 U.S.C. § 21, a person qualifies if they are a native, citizen, denizen, or subject of a hostile foreign nation, are at least fourteen years old, and have not been naturalized as a U.S. citizen.¹ The classification does not turn on how long someone has lived in the United States or whether they hold a valid visa.

Two exclusions carry real weight. Anyone who completed naturalization before hostilities began falls outside the law. So does anyone under fourteen, a floor that has been part of the Act since 1798.

“Denizen” is the term that confuses modern readers. The Act does not define it, but in eighteenth-century usage it described a status between full citizen and temporary visitor, closer to what we would now call a permanent resident of a foreign country.¹ Grouping natives, citizens, denizens, and subjects together, the statute pulls in anyone tied to the enemy government regardless of the exact nature of the tie.

What Triggers the Act

The Act activates in one of two ways. The first is a declared war: once Congress formally declares war against a foreign nation, the President can issue proclamations targeting that nation’s nationals. The second is an invasion or predatory incursion that is “perpetrated, attempted, or threatened” against U.S. territory by a foreign nation or government.¹

For more than two centuries, only the first trigger was ever used. The War of 1812, World War I, and World War II each began with a formal declaration of war, and the President in each case issued proclamations naming the enemy nationals covered. The invasion trigger was not used until March 2025, when President Trump invoked it against Tren de Aragua.²

In late-eighteenth-century usage, “invasion” and “predatory incursion” referred to military attacks. “Predatory incursion” described smaller armed raids of the kind Benedict Arnold conducted against Richmond in 1781. Whether that language reaches transnational gang activity is now one of the central legal disputes over the Act.

What the President Can Do Once It Is Invoked

After a proclamation, the executive branch gains sweeping authority over the movement, residence, and removal of alien enemies. The statute lets the President set “the manner and degree of the restraint” imposed on covered individuals, define the conditions under which they may be allowed to remain, and order the removal of those who cannot.¹

In practice, that authority has included requiring alien enemies to post financial bonds for good behavior, to report regularly to federal authorities, and to stay within specified geographic boundaries. The President can also bar them from designated areas such as coastlines or the zones around military facilities. A final catch-all provision permits “any other regulations which are found necessary” for public safety, language courts have read to grant broad discretion.¹

Enforcement runs through administrative channels rather than criminal ones. During World War II, federal agents apprehended people identified as alien enemies without the arrest warrants that ordinary criminal procedure requires, and detainees were held in internment facilities while their cases were reviewed.

A Narrow Right to Voluntary Departure

A companion statute, 50 U.S.C. § 22, provides some breathing room for alien enemies who are not personally accused of hostile conduct. If a person is not “chargeable with actual hostility, or other crime against the public safety,” the law entitles them to a reasonable period to settle their affairs and leave the country voluntarily.³

Where a treaty between the United States and the hostile nation sets a departure timeline, that treaty controls. Otherwise, the President sets “such reasonable time as may be consistent with the public safety, and according to the dictates of humanity and national hospitality.” During World War II, active combat across the Atlantic and Pacific made physical departure difficult, and the government focused on detention rather than facilitated departure.

How Courts Review Actions Under the Act

Executive actions under the Alien Enemies Act have long been treated as largely unreviewable. The controlling case is Ludecke v. Watkins (1948), in which the Supreme Court upheld the removal of a German national after the war’s active fighting had ended. The Court held that the President’s removal power under the Act is “not subject to judicial review,” and that a state of war continues for purposes of the Act until the political branches formally end it.⁴

A person detained under the Act can file a habeas corpus petition, but the questions a court will examine are few: whether the Act itself is constitutional, whether it has been properly interpreted, and whether the person actually meets the statutory definition of an alien enemy. Once those threshold questions are answered, the inquiry ends. Courts do not second-guess whether the individual actually poses a security threat, because the statute assigns that judgment to the President.⁴

Because removal under the Act is administrative, the constitutional protections that attach to criminal prosecutions do not apply. There is no right to a jury trial, no right to confront witnesses, and no right to appointed counsel. The framework reflects a deliberate wartime tradeoff between executive control over enemy nationals and ordinary judicial oversight.

What the Act Is Not: Executive Order 9066

The Alien Enemies Act is often confused with Executive Order 9066, but they are separate legal instruments that swept in different populations. The Act applies only to non-citizens of enemy nations. It could not touch someone who had been naturalized, and it could not be used against American-born citizens regardless of ancestry.

Executive Order 9066, signed in February 1942, let the military designate “military areas” and exclude any person from them. Under that authority, the military forcibly relocated roughly 120,000 people of Japanese ancestry from the West Coast, about two-thirds of whom were U.S. citizens.⁵ That mass relocation of citizens did not rest on the Alien Enemies Act. It rested on the executive order and the military’s claim of wartime necessity. If you are researching what happened to Japanese American citizens during the war, the Alien Enemies Act is not the statute that reached them.

The 2025 Invocation Against Tren de Aragua

In March 2025, President Trump issued a proclamation invoking the Alien Enemies Act on the invasion trigger for the first time. The proclamation declared that Tren de Aragua was “perpetrating, attempting, and threatening an invasion or predatory incursion” against U.S. territory, and classified Venezuelan citizens aged fourteen and older who are members of the gang as alien enemies subject to summary apprehension and removal.²

The proclamation directed the Attorney General and the Secretary of Homeland Security to carry out apprehensions and removals, and authorized the seizure and forfeiture of property “used, intended to be used, or commonly used to perpetrate the hostile activity and irregular warfare” of the gang. Compared with the World War II proclamations, which covered every national of an enemy country, the 2025 proclamation was narrower in one sense (limited to alleged gang members) and broader in another (untied to any declared war).

Trump v. J.G.G.

The proclamation was challenged almost immediately. On March 15, 2025, a federal district court in Washington, D.C. issued temporary restraining orders blocking removals. The D.C. Circuit declined to stay those orders, and the government sought emergency relief from the Supreme Court.⁶

In April 2025, the Supreme Court vacated the lower court orders on procedural grounds. Challenges to removal under the Alien Enemies Act, the Court held, must be brought through habeas corpus petitions filed in the district where the person is confined. Because the detainees were held in Texas, the D.C. courts lacked jurisdiction.⁶

The opinion did establish two protections that go beyond the World War II caselaw. The Fifth Amendment’s due process guarantee applies to individuals facing removal under the Act, entitling them to “notice and opportunity to be heard appropriate to the nature of the case.” And detainees must receive actual notice that they are subject to removal under the Act, with enough time to seek habeas relief in the proper court before being deported.⁶

The larger substantive questions are still open. No court has ruled on the merits whether gang activity by a foreign criminal organization qualifies as an “invasion or predatory incursion” under the statute, or whether the President can invoke the Act against a subset of a country’s nationals rather than the country itself. Those two questions will shape how far the Alien Enemies Act reaches in the years ahead.

1
Office of the Law Revision Counsel. 50 USC 21 – Restraint, Regulation, and Removal
2
The White House. Invocation of the Alien Enemies Act Regarding the Invasion of the United States by Tren De Aragua
3
Office of the Law Revision Counsel. 50 USC 22 – Time Allowed to Settle Affairs and Depart
4
Justia. Ludecke v. Watkins, 335 US 160 (1948)
5
National Archives. Alien and Sedition Acts (1798)
6
Supreme Court of the United States. Trump v. J.G.G.