United States v. Knox was a Supreme Court case decided in 1871. The case involved a dispute between the United States and John Knox, a former Confederate soldier. Knox had been convicted of treason for his involvement in the Civil War and was sentenced to death. However, the Supreme Court overturned his conviction, ruling that the government had failed to prove that Knox had committed any overt act of treason. The Court also held that the government had failed to prove that Knox had the requisite intent to commit treason. The Court's decision was based on the fact that Knox had not taken any action that could be considered an overt act of treason, and that he had not acted with the intent to overthrow the government. The Court's ruling was a major victory for civil liberties, as it established that the government must prove both an overt act and intent in order to convict someone of treason.

In the dissenting opinion of United States v. Knox, Justice Scalia argued that the majority’s interpretation of 18 U.S.C § 922(g)(1) was too broad and could lead to criminalizing conduct which Congress did not intend to be illegal under this statute. He noted that while it is true that a person who has been convicted of a misdemeanor crime punishable by more than two years in prison can never legally possess firearms, there are many misdemeanors for which such punishment is rarely imposed or even contemplated by legislatures when they pass laws creating these offenses. Therefore, he argued that if Congress had intended all persons convicted of any misdemeanor punishable by more than two years in prison to be prohibited from possessing firearms then it would have said so explicitly rather than leaving it up to courts to determine what types of misdemeanors should fall within this prohibition based on their own interpretations as the majority had done here.