As Article III, §2 reflects, the Framers of the Constitution intended for federal courts not to be limited to hearing only cases that arise under federal law. In addition to authorizing Congress to confer jurisdiction over disputes involving the United States, Ambassadors, Ministers and Consuls, and over admirality and maritime cases, the Constitution contemplates that federal courts could adjudicate purely state law disputes if the adverse parties are either (a) citizens of different states within the Union, (b) a State and a citizen of another State, (c) two separate States, or (d) any State or a citizen of any State and any foreign sovereign or a citizen of any foreign sovereign. Congress subsequently exercised this constitutionally delegated authority to create such pockets of jurisdiction when it passed legislation, now found at 28 U.S.C. §1332, which provides for federal subject matter jurisdiction on the basis of diversity of citizenship and alienage.
In contrast to the justification for the creation of federal question jurisdiction, neither diversity nor alienage jurisdiction is grounded on either the purported comparative competence of federal judges or the need for uniformity of result. Rather, these two related bases of federal jurisdiction historically have been predicated on the notion that since out-of-staters (either from another State or another nation) could be victimized by the “home field advantage” enjoyed by forum citizens, they deserve the opportunity to bring their claims (or, in the case of removed actions, their defenses) before a federal judge whose appointment with life tenure renders her less amenable to local prejudices, pressures, and concerns than a state magistrate.