To buttress the nation's ability to prosecute a war or armed conflict, Congress has also enacted numerous statutes which confer standby authority on the President or the executive branch and are activated by the enactment of a declaration of war, the existence of a state of war, or the promulgation of a declaration of national emergency. It (1) provides historical background on each of the declarations of war and on several major authorizations for the use of force that have been enacted; (2) analyzes the implications of declarations of war and authorizations for the use of force under both international law and domestic law; (3) lists and summarizes the more than 250 standby statutory authorities that can come into effect pursuant to a declaration of war, the existence of a state of war, and/or a declaration of national emergency; (4) describes the procedures in Congress governing the consideration of declarations of war and authorizations for the use of force, including the procedures under the War Powers Resolution; and (5) sets forth in two appendices the texts of all of the declarations of war and the major authorizations for the use of force that have been enacted. The report will be updated as circumstances warrant. Previous Declarations of War

From the Washington Administration to the present, there have been 11 separate formal declarations of war against foreign nations enacted by Congress and the President, encompassing five different wars—the War of 1812 with Great Britain, the War with Mexico in 1846, the War with Spain in 1898, the First World War, and the Second World War. In each case the enactment of a formal declaration of war has been preceded by a presidential request to Congress for such an action, either in writing or in person before a joint session of Congress. These reasons have included armed attacks on United States territory or its citizens, and attacks on or direct threats to United States rights or interests as a sovereign nation. In most cases such legislation has been preceded by a specific request by the President for such authority. Authorizations for the use of force, in contrast, have not been seen as automatically creating a state of war under international law. But an authorization for the use of force, in itself and in contrast to a declaration of war, does not trigger any of these standby authorities. On the other hand, the authorization to use force in response to the terrorist attacks of 2001 has been asserted as legal authority for executive actions in the domestic context, the validity of which remains unresolved. The War Powers Resolution

Both a declaration of war and an authorization for the use of force have significant implications with respect to the War Powers Resolution (WPR). None appear necessarily to require a declaration of war to be applicable, but a declaration can trigger their application. They do not appear to be triggered by an authorization for the use of force unless a state of war develops. Whereas, by the act of the Republic of Mexico, a state of war exists between that Government and the United States:
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled , That, for the purpose of enabling the government of the United States to prosecute said war to a speedy and successful termination, the President be, and he is hereby, authorized to employ the militia, naval, and military forces of the United States, and to call for and accept the services of any number of volunteers, not exceeding fifty thousand, who may offer their services, either as cavalry, artillery, infantry, or riflemen, to serve twelve months after they shall have arrived at the place of rendezvous, or to the end of the war, unless sooner discharged, according to the time for which they shall have been mustered into service; and that the sum of ten millions of dollars, out of any moneys in the treasury, or to come into the treasury, not otherwise appropriated, be, and the same is hereby, appropriated for the purpose of carrying the provisions of this act into effect.
From the Washington Administration to the present, Congress and the President have enacted 11 separate formal declarations of war against foreign nations in five different wars. Each declaration has been preceded by a presidential request either in writing or in person before a joint session of Congress. The reasons cited in justification for the requests have included armed attacks on United States territory or its citizens and threats to United States rights or interests as a sovereign nation.
Congress and the President have also enacted authorizations for the use of force rather than formal declarations of war. Such measures have generally authorized the use of force against either a named country or unnamed hostile nations in a given region. In most cases, the President has requested the authority, but Congress has sometimes given the President less than what he asked for. Not all authorizations for the use of force have resulted in actual combat. Both declarations and authorizations require the signature of the President in order to become law.
In contrast to an authorization, a declaration of war in itself creates a state of war under international law and legitimates the killing of enemy combatants, the seizure of enemy property, and the apprehension of enemy aliens. While a formal declaration was once deemed a necessary legal prerequisite to war and was thought to terminate diplomatic and commercial relations and most treaties between the combatants, declarations have fallen into disuse since World War II. The laws of war, such as the Hague and Geneva Conventions, apply to circumstances of armed conflict whether or not a formal declaration or authorization was issued.
With respect to domestic law, a declaration of war automatically triggers many standby statutory authorities conferring special powers on the President with respect to the military, foreign trade, transportation, communications, manufacturing, alien enemies, etc. In contrast, no standby authorities appear to be triggered automatically by an authorization for the use of force, although the executive branch has argued, with varying success, that the authorization to use force in response to the terrorist attacks of 2001 provided a statutory exception to certain statutory prohibitions.
Most statutory standby authorities do not expressly require a declaration of war to be actualized but can be triggered by a declaration of national emergency or simply by the existence of a state of war; however, courts have sometimes construed the word "war" in a statute as implying a formal declaration, leading Congress to enact clarifying amendments in two cases. Declarations of war and authorizations for the use of force waive the time limitations otherwise applicable to the use of force imposed by the War Powers Resolution.
This report provides historical background on the enactment of declarations of war and authorizations for the use of force and analyzes their legal effects under international and domestic law. It also sets forth their texts in two appendices. The report includes an extensive listing and summary of statutes that are triggered by a declaration of war, a declaration of national emergency, and/or the existence of a state of war. The report concludes with a summary of the congressional procedures applicable to the enactment of a declaration of war or authorization for the use of force and to measures under the War Powers Resolution. The report will be updated as circumstances warrant.