Even before President Trump invoked powers under the 1798 Alien Enemies Act, the historical meaning of “alien enemy” had become a topic of controversy, because the distinction between an alien enemy and an alien friend is also relevant in the context of immigration and birthright citizenship.
Largely overlooked in this debate has been the legal doctrine that defines the difference between an alien enemy and an alien friend: the doctrine of allegiance, which our Founders inherited from English law. The English doctrine closely paralleled the international law concept of the same name.
To understand the Alien Enemies Act, it is important to understand the Founding-era rules of allegiance and how they divide alien friends from alien enemies. We cannot here fully address the president’s deportation power, because the Alien Enemies Act does not authorize presidential deportation of all alien enemies—only those participating in an “invasion or predatory incursion … by a foreign nation or government.” It is nevertheless a useful starting point to recover the historical meaning of this distinction.
The doctrine of allegiance is crucial for understanding the Alien Enemies Act, but it also is crucial for understanding the Constitution itself. The meaning of many of that document’s terms rests in part on the meaning of allegiance. Examples include the Define and Punish Clause (Article I, Section 8, Clause 10), which grants power to Congress to regulate immigration and emigration; the requirement that the president be a “natural born Citizen” (Article II, Section 1, Clause 5); the provisions addressing treason (Article I, Section 6; Article II, Section 4; Article III, Section 3 & Article IV, Section 2, Clause 2); and federal and reserved state war powers (Article I, Section 8, Clause 11, Article I, Section 10, Clause 3, and others). And as the Supreme Court recognized in United States v. Wong Kim Ark (1898), allegiance also is central to the meaning of the 14th Amendment’s phrase “subject to the jurisdiction thereof”—and therefore to the meaning of birthright citizenship.
Despite its importance, few modern constitutional commentators have grasped the actual meaning of “allegiance” as the Founders understood it. In part, I think, this is because few commentators have much of a background in eighteenth-century law. In part also, it is because crucial English precedents on the subject—for example, much of Calvin’s Case (1608)—are composed partly in untranslated Latin, and, dedecore dictu, most commentators are ignorant of that language. Whatever the reasons for modern lapses, to fully understand the Constitution—or the Alien Enemies Act—you have to know the Founding-era rules of allegiance. My coauthor Andrew T. Hyman and I confirmed this while researching the scope of the war powers the Constitution reserves to the states for an article published last year in the British Journal of American Legal Studies, in which we reconstructed the Founding-era meaning of allegiance. Readers interested in more information—including some of the errors made by modern writers—may wish to consult that article.