In its 2004 decision Sosa v. Alvarez-Machain, the Supreme Court seemed to resolve the long-standing academic and judicial debate over the propriety of international law litigation under the Alien Tort Statute (ATS). A six-member court majority rejected the U.S. government’s argument that the ATS, enacted in 1789, is a jurisdictional provision that cannot be the basis for an independent cause of action under customary international law. On the other hand, the majority held that federal courts must act with great caution when recognizing causes of action under international law, for a variety of prudential and constitutional separation of powers reasons....