Article 1, Section 8, Clause 4 (Citizenship)
Joseph Story, Commentaries on the Constitution 3:§§ 1098--991833
§ 1098. The propriety of confiding the power to establish an uniform rule of naturalization to the national government seems not to have occasioned any doubt or controversy in the convention. For aught that appears on the journals, it was conceded without objection. Under the confederation, the states possessed the sole authority to exercise the power; and the dissimilarity of the system in different states was generally admitted, as a prominent defect, and laid the foundation of many delicate and intricate questions. As the free inhabitants of each state were entitled to all the privileges and immunities of citizens in all the other states, it followed, that a single state possessed the power of forcing into every other state, with the enjoyment of every immunity and privilege, any alien, whom it might choose to incorporate into its own society, however repugnant such admission might be to their polity, conveniencies, and even prejudices. In effect every state possessed the power of naturalizing aliens in every other state; a power as mischievous in its nature, as it was indiscreet in its actual exercise. In one state, residence for a short time might, and did confer the rights of citizenship. In others, qualifications of greater importance were required. An alien, therefore, incapacitated for the possession of certain rights by the laws of the latter, might, by a previous residence and naturalization in the former, elude at pleasure all their salutary regulations for self-protection. Thus the laws of a single state were preposterously rendered paramount to the laws of all the others, even within their own jurisdiction. And it has been remarked with equal truth and justice, that it was owing to mere casualty, that the exercise of this power under the confederation did not involve the Union in the most serious embarrassments. There is great wisdom, therefore, in confiding to the national government the power to establish a uniform rule of naturalization throughout the United States. It is of the deepest interest to the whole Union to know, who are entitled to enjoy the rights of citizens in each state, since they thereby, in effect, become entitled to the rights of citizens in all the states. If aliens might be admitted indiscriminately to enjoy all the rights of citizens at the will of a single state, the Union might itself be endangered by an influx of foreigners, hostile to its institutions, ignorant of its powers, and incapable of a due estimate of its privileges.
§ 1099. It follows, from the very nature of the power, that to be useful, it must be exclusive; for a concurrent power in the states would bring back all the evils and embarrassments, which the uniform rule of the constitution was designed to remedy. And, accordingly, though there was a momentary hesitation, when the constitution first went into operation, whether the power might not still be exercised by the states, subject only to the control of congress, so far as the legislation of the latter extended, as the supreme law; yet the power is now firmly established to be exclusive. The Federalist, indeed, introduced this very case, as entirely clear, to illustrate the doctrine of an exclusive power by implication, arising from the repugnancy of a similar power in the states. "This power must necessarily be exclusive," say the authors; "because, if each state had power to prescribe a distinct rule, there could be no uniform rule."
The Founders' Constitution
Volume 2, Article 1, Section 8, Clause 4 (Citizenship), Document 25
The University of Chicago Press
Story, Joseph. Commentaries on the Constitution of the United States. 3 vols. Boston, 1833.