In United States v. Billing, the Supreme Court considered whether a person could be convicted of treason for aiding Confederate forces during the Civil War. The defendant had been charged with treason after he provided supplies to Confederate troops in Virginia and was found guilty by a jury trial. On appeal, the Supreme Court held that providing aid to an enemy force is sufficient evidence of intent to betray one's country and thus can constitute treason under U.S law. The court further noted that it did not matter if this assistance was given before or after hostilities began; any act which aids an enemy power is punishable as treason regardless of when it occurred during wartime activities. In conclusion, the court affirmed Billing’s conviction for committing acts of treason against his own nation by helping its enemies in times of war

In United States v. Billing, the Supreme Court held that a federal statute which prohibited citizens from trading with Confederate states during the Civil War was constitutional. Justice Field dissented, arguing that Congress had exceeded its authority in passing such legislation because it did not fall within any of the enumerated powers granted to Congress by Article I of the Constitution. He argued further that even if this were an appropriate exercise of congressional power, it would still be unconstitutional as applied to Billing since he had acted before passage of the law and thus could not have been aware or expected to comply with its requirements. Finally, Field asserted that punishing individuals for acts committed prior to enactment violated fundamental principles of justice and fairness enshrined in both common law and natural rights theory.