The Alien Enemies Act of 1798 ("Act") allows the president to detain or deport the natives and citizens of an "enemy" nation with little if any due process. The Act is codified at 50 USC Chapter 3: Alien Enemies (also see the transcription of the original act at the bottom of this page).
When invoked by the President, the law states that "all natives, citizens, denizens, or subjects of the hostile nation or government, being males of the age of fourteen years and upwards, who shall be within the United States, and not actually naturalized, shall be liable to be apprehended, restrained, secured and removed, as alien enemies."
Under its terms the Act can be invoked via a Presidential Proclamation on two bases:
- Basis 1: "...whenever there shall be a declared war between the United States and any foreign nation or government," or
- Basis 2: When "any invasion or predatory incursion shall be perpetrated, attempted, or threatened against the territory of the United States, by any foreign nation or government..."
Regarding basis 1. The president may invoke the Alien Enemies Act under basis 1 only if war against a foreign nation or government has been declared. Only Congress has the power to declare war. The United States web page About Declarations of War by Congress relates that "Congress approved its last formal declaration of war during World War II" but that in military actions since then Congress "has agreed to resolutions authorizing the use of military force and continues to shape U.S. military policy through appropriations and oversight."
Regarding basis 2. Under basis 2, the president may invoke the Alien Enemies Act without getting Congressional approval based on an attempted, ongoing, or even threatened "invasion or predatory incursion" by a "foreign nation or government." The president has inherent authority to repel these kinds of sudden attacks - an authority that necessarily implies the discretion to decide when an invasion or predatory incursion is underway."
Note that under either basis, the law requires the hostility to be perpetrated by a "foreign nation or government."
Trump Executive Actions Invoking the Act
Trump executive actions invoking the Alien Enemies Act include:
- Proclamation of March 15, 2025, Invocation of the Alien Enemies Act Regarding the Invasion of The United States by Tren De Aragua. See NAFSA's page for more information on this proclamation.
Other Trump Executive Actions Related to "Invasion"
Other Trump executive actions invoking the concept of "invasion," though not necessarily stemming from or invoking the Alien Enemies Act, include:
- Executive Order 14159 of January 20, 2025: Protecting The American People Against Invasion. EO on whitehouse.gov | Federal Register cite: 90 FR 8443 (January 29, 2025). Among other things, directs the DHS Secretary to "ensure that the primary mission of U.S. Immigration and Customs Enforcement's Homeland Security Investigations division is the enforcement of the provisions of the INA and other Federal laws related to the illegal entry and unlawful presence of aliens in the United States and the enforcement of the purposes of this order." Note that the Student and Exchange Visitor Program (SEVP) is housed within HSI.
- Presidential Proclamation 10888 of January 20, 2025: Guaranteeing the States Protection Against Invasion. Proclamation on whitehouse.gov | Federal Register cite: 90 FR 8333 (January 29, 2025). Declares that an ongoing "invasion" is occurring at the U.S. southern border and invokes executive authority under the Constitution and immigration law to suspend the entry of migrants crossing the border illegally. The proclamation directs the Department of Homeland Security to implement broad restrictions on entry, including denying asylum claims and removing individuals without processing under standard immigration procedures. In this executive order, President Trump also invoked his authority under Article IV, Section 4 of the Constitution, which provides that "The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion..."
Background on the Alien Enemies Act
Prior to President Trump's invocation of it, the Alien Enemies Act had been implemented only three times in the history of the United States, all during three major military conflicts involving a declaration of war:
- The War of 1812 War with Britain
- The First World War
- The Second World War
During both World Wars, this Act provided the legal basis for the U.S. government to detain, remove, and impose limitations on immigrants with German, Austro-Hungarian, Japanese, and Italian heritage based on their national origins alone. The legislation is particularly notorious for its use in the internment of Japanese Americans during World War II that was facilitated by President Franklin D. Roosevelt's Executive Order 9066 of February 19, 1942.
The Alien Enemies Act is one of four 1798 acts of Congress collectively known as The Alien and Sedition Acts. The Alien Enemies Act is the only of the four acts still in effect. The Alien and Sedition Acts included:
- "Naturalization Act of 1798" of June 18, 1798 - repealed in 1802
- "Alien Act" of June 25, 1798 - expired
- "Alien Enemies Act" of July 6, 1798 - still valid law - Codified at 50 USC Chapter 3: Alien Enemies
- "Sedition Act"of July 14 1798 - expired
Transcription of the Alien Enemies Act of 1798
An Act Respecting Alien Enemies
SECTION 1. Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That whenever there shall be a declared war between the United States and any foreign nation or government, or any invasion or predatory incursion shall be perpetrated, attempted, or threatened against the territory of the United States, by any foreign nation or government, and the President of the United States shall make public proclamation of the event, all natives, citizens, denizens, or subjects of the hostile nation or government, being males of the age of fourteen years and upwards, who shall be within the United States, and not actually naturalized, shall be liable to be apprehended, restrained, secured and removed, as alien enemies. And the President of the United States shall be, and he is hereby authorized, in any event, as aforesaid, by his proclamation thereof, or other public act, to direct the conduct to be observed, on the part of the United States, towards the aliens who shall become liable, as aforesaid; the manner and degree of the restraint to which they shall be subject, and in what cases, and upon what security their residence shall be permitted, and to provide for the removal of those, who, not being permitted to reside within the United States, shall refuse or neglect to depart therefrom; and to establish any other regulations which shall be found necessary in the premises and for the public safety: Provided, that aliens resident within the United States, who shall become liable as enemies, in the manner aforesaid, and who shall not be chargeable with actual hostility, or other crime against the public safety, shall be allowed, for the recovery, disposal, and removal of their goods and effects, and for their departure, the full time which is, or shall be stipulated by any treaty, where any shall have been between the United States, and the hostile nation or government, of which they shall be natives, citizens, denizens or subjects: and where no such treaty shall have existed, the President of the United States may ascertain and declare such reasonable time as may be consistent with the public safety, and according to the dictates of humanity and national hospitality.
SEC. 2. And be it further enacted, That after any proclamation shall be made as aforesaid, it shall be the duty of the several courts of the United States, and of each state, having criminal jurisdiction, and of the several judges and justices of the courts of the United States, and they shall be, and are hereby respectively, authorized upon complaint, against any alien or alien enemies, as aforesaid, who shall be resident and at large within such jurisdiction or district, to the danger of the public peace or safety, and contrary to the tenor or intent of such proclamation, or other regulations which the President of the United States shall and may establish in the premises, to cause such alien or aliens to be duly apprehended and convened before such court, judge or justice; and after a full examination and hearing on such complaint. and sufficient cause therefor appearing, shall and may order such alien or aliens to be removed out of the territory of the United States, or to give sureties of their good behaviour, or to be otherwise restrained, conformably to the proclamation or regulations which shall and may be established as aforesaid, and may imprison, or otherwise secure such alien or aliens, until the order which shall and may be made, as aforesaid, shall be performed.
SEC. 3. And be it further enacted, That it shall be the duty of the marshal of the district in which any alien enemy shall be apprehended, who by the President of the United States, or by order of any court, judge or justice, as aforesaid, shall be required to depart, and to be removed, as aforesaid, to provide therefor, and to execute such order, by himself or his deputy, or other discreet person or persons to be employed by him, by causing a removal of such alien out of the territory of the United States; and for such removal the marshal shall have the warrant of the President of the United States, or of the court, judge or justice ordering the same, as the case may be.
APPROVED, July 6, 1798.
For more background, see:
- The Alien Enemies Act, Explained, Brennan Center for Justice, October 9, 2024.
- The Alien Enemies Act, Katherine Yon Ebright, Brennan Center for Justice, originally published October 10, 2024.