Farr, a U.S. company, contracted to buy sugar from CAV, a Cuban company owned by U.S. citizens. Because the government of Cuba nationalized its sugar industry, including CAV, it demanded that payments for sugar already shipped must be made to the Banco Nacional de Cuba. At CAV's insistence that it was the rightful owner of the sugar, and that the nationalization violated international law, Farr paid CAV. Banco Nacional sued to collect payment from Farr for the sugar delivered.
The case went to the Supreme Court, where Banco Nacional was held to be correct. On what theory would the Supreme Court base its opinion? [Banco Nacional de Cuba v. Sabbatino, 84 S. Ct. 923 (1964)]