The Slaughterhouse Cases

U.S. Citizens are Federal citizens. The only citizenship mentioned in that amendment is to “the” jurisdiction thereof, as in the Federal Government citizens of the United States.

https://supreme.justia.com/cases/federal/us/83/36/
Primary Holding:
The Privileges or Immunities Clause of the Fourteenth Amendment is limited to federal citizenship rather than extending to state citizenship.

Not only may a man be a citizen of the United States without being a citizen of a State, but an important element is necessary to convert the former into the latter. He must reside within the State to make him a citizen of it, but it is only necessary that he should be born or naturalized in the United States to be a citizen of the Union.

It is quite clear, then, that there is a citizenship of the United States, and a citizenship of a State, which are distinct from each other, and which depend upon different characteristics or circumstances in the individual.

This distinction goes all the way back to 1872. A citizen of the United States is a Federal Citizen, or a citizen of the Federal Government in Washington DC. A State Citizen, on the other hand, is a member of one of the states.