Compact Clause

Duties of tonnage

A duty of tonnage is a charge imposed for the privilege of entering, trading in, or lying in a port, measured by a vessel's capacity or functioning as a vessel-specific port charge. The Court first developed the rule in cases following Cooley v. Board of Wardens. Polar Tankers v. City of Valdez invalidated a local personal-property tax that functioned as a prohibited tonnage duty.

State military and war powers

States may not keep troops or ships of war in peacetime or engage in war without congressional consent, unless actually invaded or in imminent danger. These provisions preserve national control over war and foreign relations while allowing emergency self-defense.

Story ties the invasion/imminent-danger exception directly to a state's basic right of self-preservation, not to any general license to arm:

"[A] state may be so situated, that it may become indispensable to possess military forces, to resist an expected invasion, or insurrection. The danger may be too imminent for delay; and under such circumstances, a state will have a right to raise troops for its own safety, even without the consent of congress." — Joseph Story, Commentaries on the Constitution § 1398 (1833)

He also supplies the concrete precedent behind the implied-consent rule noted below: admitting a new state on the known footing of an existing interstate compact operates as Congress's implied consent to that compact's own terms.

"[W]here a state is admitted into the Union, notoriously upon a compact made between it and the state, of which it previously composed a part; there the act of congress, admitting such state into the Union, is an implied consent to the terms of the compact. This was true, as to the compact between Virginia and Kentucky . . . and the like rule will apply to other states, such as Maine, more recently admitted into the Union." — Joseph Story, Commentaries on the Constitution § 1399 (1833)

The Virginia convention, 14 June 1788: does "unless actually invaded" prove states retain militia power?

The state war-powers restriction drew a direct ratification-era construction dispute at the Virginia convention, argued alongside the Calling Forth Militia Clause concurrent-power debate (see that page and Guarantee Clause for the fuller exchange). John Marshall read the clause's invasion/imminent-danger exception as itself proof the states retain militia power the Calling Forth Militia Clause does not extinguish:

"But what excludes every possibility of doubt, is the last part of it — that 'no state shall engage in war, unless actually invaded, or in such imminent danger as will not admit of delay.' When invaded, they can engage in war, as also when in imminent danger. This clearly proves that the states can use the militia when they find it necessary." — John Marshall, Virginia Convention, 14 June 1788

Patrick Henry read the identical clause to the opposite effect, arguing its exception is confined to actual war with a foreign power and therefore has nothing to say about a state's power to suppress domestic insurrection at all:

"What does this relate to? Not domestic insurrections, but war. If the country be invaded, a state may go to war, but cannot suppress insurrections. If there should happen an insurrection of slaves, the country cannot be said to be invaded. They cannot, therefore, suppress it without the interposition of Congress." — Patrick Henry, Virginia Convention, 14 June 1788

George Nicholas answered Henry directly with a textual argument distinct from Marshall's, reading the restriction as confined to offensive war rather than every exercise of military force: "It must be a war with a foreign enemy that the states are prohibited from making; for the exception to the restriction proves it... They are, therefore, not restrained from quelling domestic insurrections, which are totally different from making war with a foreign power."

key-insight

Marshall and Nicholas reach the same practical conclusion (states retain power to suppress domestic insurrection) from different textual routes — Marshall reads the clause's exception itself as authorizing militia use; Nicholas reads the clause's prohibition as never having reached domestic insurrection in the first place. Henry's contrary reading is not answered by either argument on its own terms in this wiki's record, making this a genuine, unresolved three-way construction dispute over the same eleven words, parallel to the four-way Guarantee Clause dispute the same day's debate produced (see that page).

Compact Clause

The text refers broadly to any agreement or compact, but modern doctrine does not require congressional consent for every interstate arrangement. Virginia v. Tennessee held that consent is required when an agreement tends to increase state political power in a way that may encroach on federal supremacy. U.S. Steel Corp. v. Multistate Tax Commission applied that test and upheld a tax compact without congressional consent. Northeast Bancorp v. Board of Governors found no compact where reciprocal state legislation lacked classic compact features.

Congress may consent before or after a compact forms, expressly or by implication. Once Congress consents, a compact becomes federal law. Cuyler v. Adams states that transformation rule, and Tarrant Regional Water District v. Herrmann applies federal-law interpretation to an interstate water compact. Green v. Biddle also treats interstate compacts as contracts protected against state impairment.

Originalist note

The Clause reflects the founding concern that states could form alliances, port systems, or military arrangements that undermine national supremacy. On the tonnage-duty prong, the Convention record shows the Framers meant the prohibition to be close to absolute: on 15 Sept. 1787, McHenry and Carroll moved to exempt tonnage duties levied "for the purpose of clearing harbours and erecting light-houses," and Mason urged the exemption on behalf of the Chesapeake states, but Gouverneur Morris and Madison opposed it — Madison arguing that the commerce power already left states with no independent tonnage authority — and the motion failed 4-6-1, leaving only the narrower "consent of Congress" formula that survives in the text.

On the compact prong, the founding-era gloss anticipates the doctrinal test the Court would not adopt until Virginia v. Tennessee almost a century later. Story's Commentaries draws the line between the wholly-prohibited "treaty, alliance, or confederation" and the consent-conditioned "agreement or compact" using the interpretive canon noscitur a sociis:

"Perhaps the language of the former clause may be more plausibly interpreted from the terms used, 'treaty, alliance, or confederation,' . . . to apply to treaties of a political character . . . The latter clause, 'compacts and agreements,' might then very properly apply to such, as regarded what might be deemed mere private rights of sovereignty; such as questions of boundary; interests in land . . . and other internal regulations for the mutual comfort, and convenience of states, bordering on each other." — Joseph Story, Commentaries on the Constitution 3:§ 1397 (1833)

Story also states, decades before the Court did, that congressional consent to a compact "may also be implied" through subsequent congressional action (§ 1399) — the same implied-consent principle later applied in Cuyler v. Adams. Modern doctrine departs from a literal "any agreement" reading, but it preserves the original federal-supremacy concern by requiring consent only when an arrangement threatens federal primacy — a concern already present in Story's private-rights/political-character distinction.