The San Pedro case was a dispute between the United States and Mexico over ownership of a ship called the San Pedro. The claimant, Valverde, argued that he had purchased the vessel from its previous owner in 1817 before it was seized by U.S. forces during an expedition against Spanish-held territories in Florida and Louisiana later that year. The Supreme Court ultimately ruled in favor of Valverde, finding that his purchase of the ship prior to its seizure gave him superior title to any claim made by either country after it had been taken into custody. This ruling established important precedent for future cases involving property rights disputes between nations as well as individuals; namely, that when two parties have conflicting claims on a piece of property or asset, whoever can prove they acquired their interest first is entitled to superior title regardless of subsequent events or actions taken by other entities involved with said asset.

In The San Pedro case, the Supreme Court was asked to decide whether a Spanish land grant made in 1804 by the Governor of Louisiana to Don Francisco Luis Hector de Carondelet was valid. The majority opinion held that it was not valid because it had been granted after Spain ceded control of Louisiana to France and before France ceded control back to Spain. However, Justice Johnson dissented from this decision and argued that since there were no laws or regulations prohibiting such grants at the time they were issued, they should be considered valid. He further noted that if these grants are invalidated then all other similar grants would also have to be invalidated which could lead to chaos and confusion among landowners throughout the region. Therefore he concluded that since there were no legal impediments preventing them from being issued when they were issued, these land grants should remain valid despite their later transfer of sovereignty between countries.