In May 1820, the United States Congress passed a landmark amendment to the 1819 Act to Protect the Commerce of the United States and Punish the Crime of Piracy. The new statute declared that any American citizen participating in the transatlantic slave trade was legally deemed a pirate and would suffer the mandatory penalty of death upon conviction. This law fundamentally expanded federal jurisdiction over maritime activities on the high seas.
Historically, piracy was defined under universal jurisdiction as hostis humani generis—an enemy of all mankind—allowing any nation's navy to capture pirate vessels anywhere in international waters. By equating slave trading with piracy, the United States leveraged these broad admiralty powers to deploy naval squadrons off the West Coast of Africa and in the Caribbean to interdict slave ships. The legal enforcement required federal prize courts to adjudicate seized vessels, manage rescued captives, and standardise strict standards of evidence for maritime offenses.
Though political opposition hindered aggressive enforcement for decades, the law provided the essential statutory framework that eventually enabled the Lincoln administration to execute the notorious slave trader Nathaniel Gordon in 1862, demonstrating the absolute legal transformation of federal maritime authority.