Fourteenth Amendment, Section 1:
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.
Even prior to the ratification of the Fourteenth Amendment, it was a settled principle that a state could not tax land situated beyond its limits. Subsequently elaborating upon that principle, the Court has said that,
we know of no case where a legislature has assumed to impose a tax upon land within the jurisdiction of another State, much less where such action has been defended by a court. 1 Insofar as a tax payment may be viewed as an exaction for the maintenance of government in consideration of protection afforded, the logic sustaining this rule is self-evident.