By the Constitution jurisdiction in the federal courts may be founded upon either the subject-matter enumerated in Article III, or upon the character of the parties, that is, where the controversy is one to which the United States is a party, or between two or more States, between a State and citizens of another State, between citizens of different States, or between a State or a citizen thereof and foreign States, citizens or subjects.

Within the meaning of the clause of the Constitution extending the federal judicial power to suits between citizens of different States it has been held that any person who is a citizen of the United States, native or naturalized, is a citizen of the State in which he is domiciled. United States citizens domiciled in the Territories or the District of Columbia do not come within this rule.29

In Strawbridge v. Curtis30 it was held that if there be two or more joint plaintiffs and two or more joint defendants, each of the plaintiffs must, by reason of citizenship of another State, be capable of suing each of the defendants in a federal court, in order to sustain the federal jurisdiction. This doctrine, thus declared, has never been departed from.31