Throwback Thursday: Professor William Casto on the Origins of the Alien Tort Statute

In the spring of 1986, Professor William Casto published an article in the Connecticut Law Review entitled The Federal Courts’ Protective Jurisdiction Over Torts Committed in Violation of the Law of Nations. Casto’s article was the first to explore the origins of the Alien Tort Statute (ATS) in detail, and despite the many law reviewpages devoted to the question since then, it remains the leading treatment. I have recently written an essaydiscussing Casto’s article for a conference celebrating his wide-ranging scholarship.

Just six years earlier, in Filartiga v. Pena-Irala (1980), the Second Circuit began the modern era of human rights litigation in U.S. courts, holding that the ATS gave the federal courts subject matter jurisdiction over suits by non-citizen plaintiffs for human rights violations abroad. As codified today, the ATS provides: “The district courts shall have original jurisdiction of any civil action by an alien for a tort only, committed in violation of the law of nations or a treaty of the United States.”

Filartiga left several important questions unanswered, including choice of law to be applied. On remand, plaintiffs argued for the application of international law as federal common law and the district court agreed. At the same time, the source of the cause of action in ATS cases divided a panel of the D.C. Circuit in Tel-Oren v. Libyan Arab Republic (1984). Judge Bork thought that only a federal statute could provide the necessary cause of action, whereas Judge Edwards thought that the ATS itself did so.

Thus the law stood, when Casto’s article appeared. He began by tracing the history of the ATS in exhaustive detail. This history led him to other conclusions with respect to choice of law and the cause of action. He thought the First Congress, which enacted the ATS as part of the Judiciary Act of 1789, expected the law of the place where the tort occurred to govern. That law would also provide the cause of action. “Any suggestion that the [ATS] creates a federal statutory cause of action,” he wrote, “is simply frivolous.” But applying foreign law to the merits when the tort occurred abroad created an Article III problem, because its diversity and alienage grant does not extend to cases between two aliens and there appeared to be no federal question. Casto would have solved this problem with a theory of protective jurisdiction, which give his article its title.

This Throwback Thursday post looks back at Casto’s 1986 article, including its historical account, its choice of law answer, and its theory of protective jurisdiction. It also considers the course that alien tort litigation has taken over the past thirty-seven years. Finally, it suggests that things might have turned out differently if U.S. courts had listened more closely to Casto.

The Origins of the ATS

Today, the history of the ATS is familiar because of the Supreme Court’s extensive discussion in Sosa v. Alvarez-Machain (2004). But in discussing the ATS’s history, Sosa relied heavily—indeed, almost exclusively—on Casto, citing him multiple times. In 1986, the history of this provision was a blank page. Scholars knew that it came from the first Judiciary Act of 1789, but they knew virtually nothing else. Just a few years before Filartiga, Judge Henry Friendly called the ATS “a kind of legal Lohengrin; … no one seems to know whence it came.”

Casto decided to find out. He first looked to William Blackstone’s Commentaries on the Laws of England, which identified three principal offenses against the law of nations that were part of the common law: violations of safe-conducts, infringement of the rights of ambassadors, and piracy. In 1781, the Continental Congress adopted a resolution recommending that the states pass laws to punish violations of safe conducts and infringements of the rights of ambassadors, as well as other violations of the law of nations. (Congress itself had authority under the Articles of Confederation to punish piracy.) The resolution ended with a recommendation that the states permit suits for damages by the party injured.

The states largely ignored these recommendations. In 1784, a French adventurer assaulted the Secretary of the French legation, M. Marbois, on the streets of Philadelphia, a violation of the law of nations for which the United States was responsible, but which it lacked the authority to punish. The assailant was ultimately tried by the Pennsylvania Supreme Court for a criminal violation of the law of nations, which the court—following Blackstone—deemed to be part of the common law of Pennsylvania. The Marbois affair was widely discussed (Casto identifies 50 letters from 15 public figures mentioning it) and illustrated the incapacity of the national government under the Articles of Confederation to address violations of the law of nations.

The 1787 Constitution gave the new federal government authority over foreign relations that the Continental Congress had lacked. During the ratification process, an incident like the Marbois affair occurred in New York. So, the First Congress exercised its new powers to write into federal law what it recommended to the states in 1781, making violations of safe-conducts and infringements of the rights of ambassadors federal crimes and giving the federal courts jurisdiction over “all causes where an alien sues for a tort only in violation of the law of nations or a treaty of the United States.”

Casto also found a 1795 attorney general opinion by William Bradford (who prosecuted Marbois’s assailant in 1784) concerning an attack on the British colony of Sierra Leone by a French force led by an American slave trader in violation of U.S. neutrality. Bradford opined that U.S. courts would lack criminal jurisdiction over the attackers but that the injured parties could bring a suit for damages under the ATS.

Choice of Law

Bradford’s opinion gave Casto the solution to the choice of law problem for modern ATS cases in which the violation of international law occurs abroad. The reason U.S. courts would have jurisdiction over a civil action, but not a criminal one, Casto noted, was that torts were “transitory.” Under English common law, which was also American common law, a tort created a cause of action against the tortfeasor that followed him wherever he went and could be brought in any court that had jurisdiction. Such transitory torts were governed by the lex loci delicti, the law of the place of the wrong.

Anticipating concerns over the extraterritorial application of foreign law that would lead the Supreme Court to apply the presumption against extraterritoriality in Kiobel v. Royal Dutch Petroleum (2013), Casto thought that it was wrong for courts to apply U.S. domestic law to human rights violations abroad. Applying U.S. law was fine when the international law violation occurred in the United States, as in the Marbois Affair. But “[a]ctivities involving aliens in foreign countries stand on an entirely different footing…. If the United States is going to regulate the activities of citizens of foreign countries in their own countries, the President and the Congress should be the principal decisionmakers.” Applying foreign domestic law was not only consistent with the understanding of the First Congress; it also avoided the extraterritoriality problem.

The Article III Question

But solving the choice of law question created a constitutional question. Article III’s grant of diversity and alienage jurisdiction does not extend to cases between two aliens like Filartiga. The Second Circuit in Filartigabrushed this problem off by assuming that the law of nations is federal common law—a proposition that later became hotly debated—and so fell within Article III’s “arising under” grant. Casto assumed the same thing, but he wanted to apply foreign domestic law to ATS cases arising abroad.  Even if a cause of action created by federal common law arises under federal law for Article III purposes, a cause of action created by foreign domestic law would not.

The answer, he thought, was a theory of protective jurisdiction, first advanced by Herbert Wechsler in 1948. The idea was that if Congress had authority to create substantive federal rules to govern an area, it could instead create federal jurisdiction while leaving non-federal law in place. Given the strong federal interest in addressing violations of international law, Casto thought protective jurisdiction was a perfect fit for ATS cases applying foreign law.

ATS Litigation After 1986

As I have recounted elsewhere, ATS litigation did not chose the road that Casto pointed to. Lower courts tended to follow Judge Edwards in Tel-Oren and hold that the ATS itself created a cause of action. They also applied international law rather than foreign domestic law to decide the merits of the claims.

In 2004, the Supreme Court addressed the cause of action question in Sosa v. Alvarez-Machain. The plaintiff argued that the ATS created a cause of action, whereas the defendant (supported by the U.S. government) argued that the ATS was purely jurisdictional and there could be no cause of action unless Congress created one. The Supreme Court rejected both these positions, quoting Casto for the proposition that the plaintiff’s argument was “simply frivolous.” Instead, it adopted the position of an amicus brief on behalf of professors of legal history, including Casto, that relied heavily on his 1986 article. (Disclosure: I wrote the brief.) The brief argued that the First Congress expected that the common law would provide the cause of action for torts in violation of the law of nations, and Sosa held that federal courts could recognize an implied cause of action under federal common law for violations of modern international law that are as well-established as the three paradigmatic torts in violation of the law of nations that the First Congress had in mind.

No one argued in Sosa that federal courts should apply foreign domestic law, which was perhaps a mistake. After Sosa, plaintiffs pressed for more and more federal common law in ATS cases, particularly to govern aiding and abetting liability in suits against corporations. The more U.S. law was applied, the more concerns over extraterritoriality grew.

The end of this story is well known. In Kiobel v. Royal Dutch Petroleum (2013), the Supreme Court applied the presumption against extraterritoriality to the ATS cause of action, limiting it to claims that “touch and concern” the United States. In Nestlé USA, Inc. v. Doe (2021), it went further, seeming to require substantial tortious conduct in the United States, a holding that would preclude cases like Filartiga that arise abroad.

Because federal courts did not apply foreign domestic law, they had no occasion to consider Casto’s theory of protective jurisdiction. In fact, the federal courts have really never addressed the Article III question, although the Supreme Court has now decided two ATS cases between aliens on the merits (Kiobel and Jesner v. Arab Bank (2018)), which it could not have done without Article III jurisdiction. The best explanation, it seems to me, is that the Court views international law as part of the “Laws of the United States” for Article III purposes, which, I have argued, is also the original understanding.

The Road Not Taken

I have previously suggested that if U.S. courts had followed Casto and applied foreign domestic law to human rights claims that arise abroad, the ATS story would have ended differently. It seems clear that the Supreme Court would not have applied the presumption against extraterritoriality to the ATS cause of action, since there would have been no ATS cause of action to begin with.

I doubt the Supreme Court would have adopted Casto’s theory of protective jurisdiction if ATS cases had taken the foreign-law road. It has never found occasion to do so. It might have held that alienage jurisdiction is the only possibility and limited ATS suits to claims against U.S. citizens as Curt Bradley and A.J. Belia and Brad Clark have argued. Or it might have held that international law is part of the “Laws of the United States” under Article III (which, I repeat, is the original understanding) and found arising under jurisdiction because the ATS requires a threshold determination of a federal question—a violation of the law of nations—before reaching the merits. It could have followed Verlinden v. Central Bank of Nigeria (1983) as a model, since that case did something similar to sustain the constitutionality of suits between two aliens under the Foreign Sovereign Immunities Act.


Although there have been proposals to amend the ATS to apply extraterritorially, most human rights litigation today is proceeding under federal statutes like the Torture Victim Protection Act (TVPA) or the Trafficking Victims Protection Reauthorization Act (TVPRA).

But Casto’s 1986 article still has much to teach us about the founding generation’s concern with violations of international law, about choice of law both then and now, and about the limits and possibilities of Article III. Casto not only answered Judge Friendly’s question about where the ATS came from; he also anticipated questions that would arise in ATS litigation years later. It is rare to find an article that looks both backward and forward with such clear vision.