The Framers of the Constitution vested in Congress the sole and exclusive authority to initiate military hostilities, including full-blown, total war, as well as lesser acts of armed force, on behalf of the American people. The constitutional grant to Congress of the war power, which Justice William Paterson described in United States v. Smith (1806) as "the exclusive province of Congress to change a state of peace into a state of war," constituted a sharp break from the British model. The Framers were determined to deny to the president what Blackstone had assigned to the English King—"the sole prerogative of making war and peace." The president, in his role as commander in chief, was granted only the authority to repel invasions of the United States. But what the Framers sought to deny to the president has become a commonplace. Indeed, executive usurpation of the war power in the period since World War II has become a dominant characteristic of American foreign relations as presidents have routinely committed acts of war without congressional authorization.
The war clause of the Constitution provides: "The Congress shall have power … to declare War [and] grant Letters of Marque and Reprisal." On 29 May, in an early debate in the Constitutional Convention on the repository of the war power, a clear understanding developed among the delegates that the power of "war and peace"—the power to initiate war—did not belong to the executive but to the legislature. On 6 August the Committee of Detail circulated a draft constitution that granted Congress the power to "make" war. This bore sharp resemblance to the Articles of Confederation, which vested the "sole and exclusive right and power of determining on peace and war" to the Continental Congress. When the war clause was considered in debate on 17 August, the familiar voice from South Carolina, Charles Pinckney, was initially reluctant to place the power in the House of Representatives: "Its proceedings were too slow…. The Senate would be the best depository, being more acquainted with foreign affairs, and most capable of proper resolutions." Another South Carolinian, Pierce Butler, startled the convention when he announced that he "was for vesting the power in the President, who will have all the requisite qualities, and will not make war but when the nation will support it." Butler's opinion shocked Elbridge Gerry of Massachusetts, who declared that he "never expected to hear in a republic a motion to empower the Executive alone to declare war." Butler stood alone in the convention. There was no support for his opinion and no second to his motion.
The proposal of the Committee of Detail to vest Congress with the power to "make" war proved unsatisfactory to Madison and Gerry. In what must be regarded as one of the most famous joint resolutions in American history, Madison and Gerry moved to substitute "declare" for "make," and they explained that the purpose of the motion was to allow the president "to repel sudden attacks." The meaning of the motion was clear. The power to initiate war was granted to Congress, with the reservation that the president need not await authorization from Congress to repel a sudden attack on the United States. There was no quarrel whatever with respect to the sudden-attack provision, but there was some question as to whether the substitution of "declare" for "make" would effect the intention of Madison and Gerry. Roger Sherman of Connecticut thought the joint motion "stood very well." He believed that it permitted the executive "to repel and not commence war." Virginia's George Mason announced that he "was against giving the power of war to the Executive, because not safely to be trusted with it," then said he preferred "declare" to "make." The adoption of the Madison-Gerry proposal made it clear that Congress alone possessed the authority to initiate war. The warmaking power was specifically denied to the president; he was given only the authority to repel sudden attacks against the United States. No delegate to the Philadelphia convention and no member of any state ratifying convention contested this understanding. James Wilson, one of the most penetrating constitutional theorists of the founding generation, captured the precise intent of the convention: this system "will not hurry us into war; it is calculated to guard against it. It will not be in the power of a single man, or a single body of men, to involve us in such distress."
At the time of the convention, the phrase "declare war" enjoyed a settled understanding and an established usage. As early as 1552 the verb "declare" had become synonymous with the verb "commence"; they both implied the initiation of hostilities. This was the established usage in international law as well as in England, where the terms to "declare" war and to "make" war were used interchangeably. This practice was thoroughly familiar to the Framers. Given the equivalence of commence and declare, it is clear that a congressional declaration of war would institute military hostilities. According to international law commentators at the time of the founding, a declaration of war was desirable because it announced the institution of a state of war, and the legal consequences it entailed, to the adversary, to neutral nations, and to citizens of the sovereign initiating the war. Indeed, this is the essence of a declaration of war: notice by the proper authority of intent to convert a state of peace into a state of war. But all that is required under American law is a joint resolution or an explicit congressional authorization of the use of military force against a named adversary. This can come in the form of a "declaration pure and simple," or in a "conditional declaration of war." There are also two kinds of war, those that U.S. courts have termed "perfect," or general, and those labeled "imperfect," or limited, wars. In 1782, in Miller v. The Ship Resolution, the federal court of appeals, established by the Continental Congress, stated: "The writers upon the law of nations, speaking of different kinds of war, distinguish them into perfect and imperfect: A perfect war is that which destroys the national peace and tranquillity, and lays the foundation of every possible act of hostility. The imperfect war is that which does not entirely destroy the public tranquillity, but interrupts it only in some particulars, as in the case of reprisals."
It was decided at the dawn of the Republic that the power of determining perfect and imperfect war lay with Congress. In Talbot v. Seeman (1801), Chief Justice John Marshall wrote for the Court that the war power of Congress comprises the power "to declare a general war" and also to "wage a limited war." The power of Congress to authorize limited war is, of course, a necessary concomitant of its power to declare general war. If the president might authorize relatively minor acts of war or perhaps covert military operations in circumstances not demanding full-blown war, that power could be wielded in a way that would easily eviscerate the Constitution's placement of the war power in Congress. But the Framers withheld from the president the power to work such mischief. The Constitution granted the executive only the authority to respond defensively to the initiation of war through sudden attack upon the United States. In United States v. Smith (1806), Justice William Paterson of the Supreme Court, who had been a delegate to the Constitutional Convention from New Jersey, explained that, in the event of an invasion of the United States, it would be lawful for the president to resist such invasion for the "plain reason that a state of complete and absolute war exists between the two nations. In the case of invasive hostilities, there cannot be war on the one side and peace on the other…. There is a manifest distinction between our going to war with a nation at peace, and a war being made against us by an actual invasion, or a formal declaration. In the former case, it is the exclusive province of Congress to change a state of peace into a state of war." But the president's power of self-defense does not extend to foreign lands. The Framers did not give the president the authority to intervene in foreign wars, or to choose between war and peace, or to identify and commence hostilities against an enemy of the American people. Nor did they empower him to initiate force abroad on the basis of his own assessments of U.S. security interests. These circumstances involve choices that belong to Congress, under its exclusive province to change a state of peace into a state of war.
All of the offensive powers of the nation, then, were located in Congress. Consistent with this constitutional theory, the convention gave to Congress the power to issue "letters of marque and reprisal." Dating back to the Middle Ages when sovereigns employed private forces in retaliation for an injury caused by the sovereign of another state or his subjects, the practice of issuing reprisals gradually evolved into the use of public armies. By the time of the convention the Framers considered the power to issue letters of marque and reprisal sufficient to authorize a broad spectrum of armed hostilities short of declared war. In other words, it was regarded as a species of imperfect war.