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.
We think this distinction and its explicit recognition in this Amendment of great weight in this argument, because the next paragraph of this same section, which is the one mainly relied on by the plaintiffs in error, speaks only of privileges and immunities of citizens of the United States, and does not speak of those of citizens of the several states. The argument, however, in favor of the plaintiffs, rests wholly on the assumption that the citizenship is the same and the privileges and immunities guaranteed by the clause are the same.
The language is, "No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States." It is a little remarkable, if this clause was intended as a protection to the citizen of a State against the legislative power of his own State, that the word citizen of the State should be left out when it is so carefully used, and used in contradistinction to citizens of the United States in the very sentence which precedes it. It is too clear for argument that the change in phraseology was adopted understandingly and, with a purpose.
Of the privileges and immunities of the citizen of the United States, and of the privileges and immunities of the citizen of the State, and what they respectively are, we will presently consider; but we wish to state here that it is only the former which are placed by this clause under the protection of the Federal Constitution, and that the latter, whatever they may be, are not intended to have any additional protection by this paragraph of the amendment.
The Slaughterhouse Cases, 83 US 36 (1873).