citizen of the United States
The term US Citizen is a corporate term. There was no such thing as a United States Citizen prior to the civil war. The corporate term technically means “an employee of the UNITED STATES CORPORATION“. When you sign forms that declare that you are a US Citizen you are voluntarily committing to a contract (ie, federal taxes 1040). The corporation is not obligated to tell you that you are not a US Citizen. You volunteered for the contract.