Article I, Section 8, Clause 11:

[The Congress shall have Power . . . ] To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water; . . .

The Supreme Court has long construed the Declare War Clause to mean not only that Congress can issue formal declarations of war, but also that it can authorize the use of armed force for more limited operations short of a full-scale war.1 Congress has, on various occasions, passed what have become known as authorizations for the use of military force (or AUMFs), which permit the President to use United States military forces in pursuit of set objectives and within defined parameters.2 Early examples include congressional authorization to protect American commercial vessels from pirates and hostile foreign countries.3 Since the Second World War, Congress has not formally declared war, and AUMFs have become its predominant method to authorize hostilities. For example, Congress passed and the President signed into law statutory authorization during the Vietnam War, the Persian Gulf War of 1991, the post-September 11, 2001 invasion of Afghanistan, and the 2003 Iraq War.4

Several reasons account for the change in practice. Alexander Hamilton observed as early as 1787 that formal declarations of war had fallen into disuse in international practice.5 Other aspects of the change can be attributed to 20th century developments. For much of the United States’ history, international law treated war as a legal and legitimate method for achieving foreign policy goals under certain conditions,6 but the Charter of the United Nations (UN) fundamentally restructured the international legal regime related to use of force.7 The UN Charter prohibits war as a foreign-affairs strategy by barring countries from using military force unless in response to armed attack or under an authorization from the U.N. Security Council.8 As a result of these and other international legal developments, declarations of war have become anachronistic in modern international law and relations.9

Footnotes

1

See, e.g., Talbot v. Seeman, 5 U.S. (1 Cranch) 1, 28 (1801) ( “[C]ongress may authorize general hostilities . . . or partial hostilities” ); Bas v. Tingy, 4 U.S. (4. Dall.) 37, 43 (1800) (opinion of Chase, J.) ( “Congress is empowered to declare a general war, or congress may wage a limited war; limited in place, in objects, and in time.” ).

2

See Jennifer K. Elsea & Matthew C. Weed, Cong. Rsch. Serv., RL31133, Declarations of War and Authorizations for the Use of Military Force: Historical Background and Legal Implications 5–18 (2014), >https://crsreports.congress.gov/product/pdf/RL/RL31133/17.

3

Act of May 28, 1798, 2 Stat. 561; Act of July 9, 1798, 2 Stat. 578; Act of February 6, 1802, 2 Stat. 129, Act of March 3, 1815, 3 Stat. 230; Act of March 3, 1815, 3 Stat. 230.

4

See, e.g., Authorization for Use of Military Force, Pub. L. No. 107-40, 115 Stat. 224 (2001).

5

The Federalist No. 25 (Alexander Hamilton) ( “the ceremony of a formal denunciation of war as of late fallen into disuse” ).

6

See, e.g., 2 Charles Cheney Hyde, International Law Chiefly as Interpreted and Applied by the United States 189, § 593 (1922) ( “It always lies within the power of a State to endeavor to obtain redress for wrongs, or to gain political or other advantages over another, not merely by the employment of force, but also by direct recourse to war.” ); The Federalist No. 3 (John Jay) (describing treaty violations as “just causes of war” ). The movement to renounce war as instrument of foreign policy emerged after World War I. See Curtis A. Bradley, International Law in the U.S. Legal System 282 (1st ed. 2013); CRS Report RL31133, supra note 2, at 20–21.

7

UN Charter. See also .

8

See UN Charter, art. 2(4) (prohibiting the “threat or use of force against the territorial integrity or political independence of any state” ); id. art. 42 (permitting the UN Security Council to “take such action by air, sea, or land forces as may be necessary to maintain or restore international peace and security” ); id. art. 51 (preserving UN member states “inherent right of individual or collective self-defense if an armed attack occurs” ).

9

See CRS Report RL31133, supra note 2, at 20–21.