In 1798, Congress passed the Alien Enemies Act (AEA), which provides that during a state of “declared war,” or when “any invasion or predatory incursion is perpetrated, attempted, or threatened against the territory of the United States by any foreign nation or government,” the President can restrain and remove “all natives, citizens, denizens, or subjects of the hostile nation or government” as “alien enemies.” As the text of the AEA makes explicit, the President can only invoke the AEA’s sweeping authorities under certain circumstances and against certain people.

On March 14, 2025, President Trump invoked the AEA to address what he is calling the “Invasion of the United States by Tren de Aragua,” a criminal cartel with supposed ties to the Venezuelan government. The next day, the administration sent 251 Venezuelan immigrants detained in the United States to a maximum-security prison, CECOT, in El Salvador. It did so without giving any of them their constitutionally mandated day in court. Four months later, they were finally released. As Human Rights Watch recently reported, the Venezuelan men held at CECOT were subject to inhumane conditions.

A group of Venezuelan citizens detained in Texas challenged their threatened removal to the same notorious foreign prison. In June 2025, CAC filed an amicus brief in the Fifth Circuit supporting their challenge. In September 2025, a panel of the Fifth Circuit granted petitioners a preliminary injunction. Citing our brief, the court analyzed the AEA’s history and concluded that the Trump administration had unlawfully invoked the Act. After the government filed a petition for en banc rehearing, the full Fifth Circuit agreed to rehear the case and, on November 13, 2025, CAC filed an amicus brief in support of the group of Venezuelan citizens.

The lawmakers who passed the AEA in 1798 understood the terms “nation” and “government” to be defined by the law of nations, a set of international norms that governed foreign relations between nations at the time. The law of nations set two interrelated qualifications for any entity to be considered a nation or government: self-definition and foreign recognition. An entity had to hold itself as acting on behalf of a group of people living in a defined territory. It also had to be recognized by other nations as speaking on their people’s behalf on the international stage. These were the very qualities that the Founders thought were necessary for the American Revolution to turn thirteen colonies into a new nation.

The AEA’s history underscores why the Act can only be invoked against nations or governments that meet these qualifications. The AEA was passed in response to ongoing hostilities with one “foreign nation or government” in particular—the French Republic. In 1798, the United States was in the midst of a naval conflict, known as the Quasi War, with this erstwhile ally. In response, Congress passed the AEA and its counterpart, the notorious Alien Friends Act. The Alien Friends Act granted the President sweeping power to detain and expel any noncitizen deemed “dangerous to the peace and safety of the United States.” It was immediately attacked as unconstitutional and allowed to lapse in disgrace.

The AEA, by contrast, was widely considered constitutional. The reason for this disparity was simple: the AEA was understood to be an extension of Congress’s power to declare war. During a state of war, as James Madison explained, Congress had the power “under the law of nations” to hold foreign citizens accountable for the belligerent actions of their home country. But only a nation or government under the law of nations—an entity that claimed the authority to act on its peoples’ behalf and was recognized as having that authority—could demand the sort of allegiance from its people that would justify holding them personally accountable for their sovereign’s actions during war.

This is a high bar. That is why the AEA has been invoked just three times: during the War of 1812, World War I, and World War II. And each time, the United States was in a state of war against an entity that both held itself out and was formally recognized as a sovereign nation or government acting on behalf of its people in its territory.

The government now concedes that Tren de Aragua is not a “nation or government” within the meaning of the AEA. It has instead argued in this litigation that Tren de Aragua is so entwined with Venezuela as to effectively function as a “hybrid criminal state.” But that claim is at odds with the President’s recent determination—made explicit in a notice to Congress—that TdA is actually a non-state armed actor that he claims is engaged in a non-state armed conflict. Since September 2025, the Trump Administration has been carrying out a campaign of lethal strikes on alleged drug smugglers in the Caribbean. In a report to Congress, the President claimed that these vessels were operated by Tren de Aragua and that he had the authority to attack them because they were non-state actors in a non-state armed conflict, rather than any part of a “hybrid criminal state.” The President cannot have it both ways.

Even putting these conflicting claims aside, the President’s invocation of the AEA would still fail. The government argues that Tren de Aragua is essentially a privateer acting on behalf of the Venezuelan government. But TdA does not have the sort of formal authorization to act on behalf of Venezuela that privateers did when the AEA was enacted.

Finally, even if Tren de Aragua were acting at Venezuela’s behest, that would still only justify an invocation against Venezuela, not TdA. The requirement that the AEA be invoked against a “foreign nation or government” cannot be written out of the statute. Under the law of nations, only a presidential proclamation against the hostile actions of a nation or government could justify holding every citizen liable as “alien enemies.” That is why, in its almost 250-year history, the AEA has only ever been invoked against all citizens of a foreign nation or government, not a subset of its citizens.