In April 1800, during the undeclared Quasi-War between the United States and France, the American armed vessel Trumbull captured the French schooner Peggy as a maritime prize. A U. S.
circuit court ruled the capture lawful, ordering the schooner to be condemned and sold for profit. However, while the owners appealed the decision to the U. S.
Supreme Court, President John Adams signed the Convention of 1800 with France, which stipulated that any captured property not yet definitively condemned must be returned. In 1801, Chief Justice John Marshall delivered the opinion in United States v. Schooner Peggy, ruling that courts must apply the law in effect at the time of their judgment, even if a new treaty retroactively alters existing legal rights before a final judgment is rendered.
Marshall articulated that while retroactive legislation is generally disfavored, treaties made under executive authority override pending judicial claims if explicitly drafted to apply retroactively to non-final judgments.