A declaration of war is a formal declaration issued by a national government indicating that a state of war exists between that nation and another. A document by the Federation of American Scientists gives an extensive listing and summary of statutes which are automatically engaged upon the United States declaring war.
For the United States, Article One, Section Eight of the Constitution says "Congress shall have power to ... declare War." However, that passage provides no specific format for what form legislation must have in order to be considered a "declaration of war" nor does the Constitution itself use this term. In the courts, the United States Court of Appeals for the First Circuit, in Doe v. Bush, said: "[T]he text of the October Resolution itself spells out justifications for a war and frames itself as an 'authorization' of such a war." in effect saying an authorization suffices for declaration and what some may view as a formal congressional "Declaration of War" was not required by the Constitution.
The last time the United States formally declared war, using specific terminology, on any nation was in 1942, when war was declared against Axis-allied Hungary, Bulgaria, and Romania, because President Franklin Roosevelt thought it was improper to engage in hostilities against a country without a formal declaration of war. Since then, every American president has used military force without a declaration of war.
This article will use the term "formal declaration of war" to mean congressional legislation that uses the phrase "declaration of war" in the title. Elsewhere, this article will use the terms "authorized by Congress," "funded by Congress" or "undeclared war" to describe other such conflicts.
The United States has formally declared war against foreign nations in five separate wars, each upon prior request by the President of the United States. Four of those five declarations came after hostilities had begun. James Madison reported that in the Federal Convention of 1787, the phrase "make war" was changed to "declare war" in order to leave to the Executive the power to repel sudden attacks but not to commence war without the explicit approval of Congress. Debate continues as to the legal extent of the President's authority in this regard.
Public opposition to American involvement in foreign wars, particularly during the 1930s, was expressed as support for a Constitutional Amendment that would require a national referendum on a declaration of war. Several Constitutional Amendments, such as the Ludlow Amendment, have been proposed that would require a national referendum on a declaration of war.
After Congress repealed the Gulf of Tonkin Resolution in January 1971 and President Richard Nixon continued to wage war in Vietnam, Congress passed the War Powers Resolution (Pub.L. 93–148) over the veto of Nixon in an attempt to rein in some of the president's claimed powers. The War Powers Resolution proscribes the only power of the president to wage war which is recognized by Congress.
The table below lists the five wars in which the United States has formally declared war against eleven foreign nations. The only country against which the United States has declared war more than once is Germany, against which the United States has declared war twice (though a case could be made for Hungary as a successor state to Austria-Hungary).
In World War II, the Japanese attacked Pearl Harbor on December 7, 1941. Germany and Italy, led respectively by Adolf Hitler and Benito Mussolini, declared war on the United States, and the U.S. Congress responded in kind.
|War||Declaration||Opponent(s)||Date of declaration||Votes||President||Details of Authorization||Result|
|War of 1812||Declaration of War upon the U.K.||United Kingdom and its dependencies||June 18, 1812||19–13||79–49||James Madison||Madison requested the declaration citing the Royal Navy's impressment of U.S. citizens and violation of American neutrality during the Napoleonic Wars. The declaration was supported by the Democratic-Republican and "War Hawk" Members of Congress and opposed by the Federalist Party.||Treaty of Ghent (December 24, 1814)|
|Mexican–American War||"An Act providing for the Prosecution of the existing War between the United States and the Republic of Mexico."||Mexico||May 13, 1846||40–2||173–14||James K. Polk||Polk requested the declaration citing territorial disputes with the Mexican government refused to recognize the Rio Grande as the Mexico–United States border after the Texas Revolution and US annexation of Texas. Mexican President José Joaquín de Herrera refused to enter negotiations with U.S. ambassador John Slidell, and the Mexican Army attacked General Zachary Taylor's U.S. Army forces in the disputed area. The declaration was opposed by the Whig Party which viewed the war as a pretext for the Democratic Party and the South to add more slave states. ||Treaty of Guadalupe Hidalgo (February 2, 1848)|
|Spanish–American War||Declaration of War upon Spain||Spain||April 25, 1898||42–35||310–6||William McKinley||McKinley requested a declaration of war citing the sinking of the USS Maine in Havana Harbor after years of growing tensions during the Cuban War of Independence, which was blamed on Spain. Unlike other declarations, it occurred after the US issued an ultimatum demanding the Spanish Empire grant independence to Cuba.||Treaty of Paris (December 10, 1898)|
|World War I||Declaration of War upon Germany||Germany||April 6, 1917||82–6||373–50||Woodrow Wilson||Wilson requested a declaration of war citing the Imperial German Navy's resumption of unrestricted submarine warfare and the Zimmermann Telegram offering Mexico a return of the Mexican Cession if it allied with the Central Powers and invaded the United States.||Knox–Porter Resolution (July 1921)|
1921 U.S.–German Peace Treaty (August 25, 1921)
|Declaration of War upon Austria-Hungary||Austria-Hungary||December 7, 1917||74–0||365–1||Wilson requested a declaration of war because of its alliance with Germany and participation in attacks on United States soldiers and civilians, including the Austro-Hungarian Navy's complicity in submarine attacks on U.S. shipping.||1921 U.S.–Austrian Peace Treaty (August 24, 1921), 1921 U.S.–Hungarian Peace Treaty (August 29, 1921)|
|World War II||Declaration of War upon Japan||Japan||December 8, 1941||82–0||388–1||Franklin D. Roosevelt||Roosevelt requested a declaration of war citing the Imperial Japanese Armed Forces' attack on the United States Pacific Fleet in the Pearl Harbor bombing several days earlier. Approved near-unanimously with only one dissenting vote in the entire Congress from Jeannette Rankin.||Surrender of Japan V-J Day, Japanese Instrument of Surrender (September 2, 1945), Treaty of San Francisco (September 8, 1951)|
|Declaration of War upon Germany||Germany||December 11, 1941||88–0||393–0||Roosevelt requested a declaration of war in response to the German declaration of war against the United States. Approved unanimously with no dissenting votes.||German Instrument of Surrender (May 8, 1945), V-E Day, Treaty on the Final Settlement with Respect to Germany (September 12, 1990), Treaty of Vienna with Austria (May 15, 1955)|
|Declaration of War upon Italy||Italy||90–0||399–0||Roosevelt requested a declaration of war in response to the Italian declaration of war on the United States. Approved unanimously with no dissenting votes.||Armistice of Cassibile (September 3, 1943) |
Treaty of Peace with Italy, 1947 Paris Peace Treaties (February 10, 1947)
|Declaration of War upon Bulgaria||Bulgaria||June 5, 1942||73–0||357–0||Roosevelt requesting a declaration of war citing the three countries' participation in the Axis powers with Germany and Italy.|
|Declaration of War upon Hungary||Hungary||360–0|
|Declaration of War upon Romania||Romania||361–0|
In other instances, the United States has engaged in extended military combat that was authorized by Congress.
|War or conflict||Opponent(s)||Initial authorization||Votes||President||Details of Authorization||Result|
|Quasi-War||France||An Act further to protect the commerce of the United States
July 9, 1798
|18–4||John Adams||Adams requested legislation allowing the United States Navy to defend American shipping after repeated attacks by the French Navy during the French Revolutionary Wars.||Treaty of Mortefontaine|
|First Barbary War|| Morocco
||"An Act for the Protection of the Commerce and Seamen of the United States, Against the Tripolitan Cruisers", 2 Stat. 129, February 6, 1802||Thomas Jefferson||President Jefferson requested legislation allowing the U. S. Navy to defend shipping in the Mediterranean Sea from Tripolitanian vessels.||War ended 1805|
|Second Barbary War||"An Act for the protection of the commerce of the United States against the Algerine cruisers", 3 Stat. 230, May 10, 1815||James Madison||Madison requested a declaration of war against Algiers citing attacks on U.S. shipping in the Mediterranean. Congress rejected the request for a formal war declaration but ratified legislation allowing the U.S. Navy to defend U.S. commerce.||War ended 1816|
|Enforcing 1808 slave trade ban; naval squadron sent to African waters to apprehend illegal slave traders||Slave traders||"Act in addition to the acts prohibiting the Slave Trade", 3 Stat. 532, 1819||James Monroe||1822 first African-American settlement founded in Liberia, 1823 U.S. Navy stops anti-trafficking patrols|
|Suppression of Piracy||Pirates||1819||James Monroe||The United States Congress passed legislation allowing the United States Navy to suppress piracy in response to the rise in piracy in Latin America and the Caribbean after the Spanish American wars of independence, which was later permanently codified as Title 33 of the United States Code.|
|Redress for attack on U.S. Navy's USS Water Witch||Paraguay||1858.||James Buchanan|
|Mexican Revolution||Mexico||H.J.R. 251, 38 Stat. 770
April 22, 1914
|337–37||Woodrow Wilson||Force withdrawn after six months. However, the Joint Resolution was likely used to authorize the Pancho Villa Expedition. In the Senate, "when word reached the Senate that the invasion had gone forward before the use-of-force resolution had been approved, Republicans reacted angrily" saying it was a violation of the Constitution, but eventually after the action had already started, a resolution was passed after the action to "justify" it since Senators did not think it was a declaration of war.|
|Russian Civil War||1918||Woodrow Wilson|
|Lebanon crisis of 1958||Lebanese Opposition||H.J. Res. 117, Public Law 85-7, Joint Resolution "To promote peace and stability in the Middle East", March 9, 1957||72–19||355–61||Dwight D. Eisenhower||Eisenhower requested a legislation allowing U.S. economic and military assistance to the Middle East during the Cold War, including the ability to deploy the military in response to threatened Communist takeovers.||U.S. forces withdrawn, October 25, 1958|
||Gulf of Tonkin Resolution, August 7, 1964||88–2||416–0||Lyndon B. Johnson||Johnson requested authorization for a military deployment to defend South Vietnam and U.S. military forces already stationed there from under SEATO collective security obligations, citing alleged Vietnam People's Navy attacks on United States Navy warcraft including the USS Maddox in the Gulf of Tonkin incident. Congress responded with the Gulf of Tonkin Resolution.||U.S. forces withdrawn under terms of the Paris Peace Accords signed January 27, 1973|
|Multinational Force in Lebanon||Shia and Druze militias; Syria||S.J.Res. 159
September 29, 1983
|54–46||253–156||Ronald W. Reagan||Reagan announced the deployment of a small United States Marine Corps contingent of forces for peacekeeping in the Lebanese Civil War, claiming they would supervise the PLO withdrawal from Beirut and provide law enforcement, but not participate in direct combat. After Congress invoked the War Powers Resolution it and the Reagan administration negotiated a resolution allowing the marines to remain in Lebanon for 18 months.|
|Persian Gulf War||Ba'athist Iraq||H.J.Res. 77
January 12, 1991.
|52–47||250–183||George H.W. Bush||Bush announced the deployment of 330,000 United States Armed Forces troops to Saudi Arabia in response to the Iraqi invasion of Kuwait and began diplomatic overtures to form an international coalition to defend the Arab states of the Persian Gulf. Congress approved an Authorization for Use of Military Force against Ba'athist Iraq to liberate Kuwait under United Nations Security Council Resolution 678.||The United Nations Security Council drew up terms for the cease-fire, April 3, 1991. The administration of George W. Bush later argued that the AUMF never expired during the build-up to the Iraq War. The United States House of Representatives voted to repeal it in 2021.|
|War on Terror|| Afghanistan
Harakat Ahrar al-Sham al-Islamiyya
High Council of the Islamic Emirate
|S.J. Res. 23
September 14, 2001
|98–0||420–1||George W. Bush||Bush successfully requested a congressional authorizing the President of the United States to use military force against "those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001" as well as governments which sheltered them such as the First Islamic Emirate of Afghanistan. It also allowed the President to use force to prevent future acts of terrorism. Since then the authorization has been invoked in conflicts in 22 countries against the original perpetrator of 9/11 al-Qaeda as well as other organizations such as Al-Shabaab, the Taliban, and the Islamic State. The authorization is also notable in that it delegated war powers related to terrorism from Congress to the President, and allowed the United States to make war against individuals and organizations in addition to sovereign states. The Supreme Court ruled in Hamdi v. Rumsfeld that the authorization enabled the President to detain individuals, including U.S. citizens, as enemy combatants, although it granted detainees to challenge this status in U.S. courts and further ruled in Hamdan v. Rumsfeld that they were protected by laws of war such as the Geneva Conventions and the Uniform Code of Military Justice.||The Global War on Terror is ongoing. |
The War in Afghanistan (2001–2021), that was carried out by the United States under the Global War on Terror's general authorization for use of military force, came to an end on August 30, 2021 with the total withdrawal of the American Forces from Afghanistan under the terms of the Doha Peace Agreement signed on February 29, 2020. The U.S. disengagement from Afghanistan resulted in the Fall of Kabul to the Taliban on August 15, 2021 and in a broad re-establishment of the status quo ante bellum. The U.S. backed Islamic Republic of Afghanistan collapsed even before the completion of the American withdrawal, and the Taliban victory led to the restoration of the Islamic Emirate of Afghanistan.
Other U.S. military campaigns that are legally based on the Global War on Terror's general authorization for use of military force include the ongoing American-led intervention in the Syrian civil war that was initiated on September 22, 2014 under President Barack Obama's administration. In spite of a significant drawdown of U.S. ground forces in Syria at the direction of President Donald Trump in 2019, the United States retains a residual presence of about 600 military personnel in Syria, and continues to conduct airstrikes against Iranian-supported militias as of 2021.
|Iraq War||Ba'athist Iraq||H.J. Res. 114,
March 3, 2003
|77–23||296–132||George W. Bush||During the Iraq disarmament crisis Bush successfully requested an authorization of military force against Iraq citing alleged allegations of violations of United Nations Security Council resolutions including the ceasefire with Kuwait, allegations of illegal weapons of mass destruction programs, allegations of the sheltering of al-Qaeda members in the country. The Bush administration also claimed that the conflict was sanctioned by the 1991 AUMF against Iraq and by the Iraq Liberation Act of 1998 designating the overthrow of Saddam Hussein's dictatorship as a goal of U.S. foreign policy.||Ba'athist Iraqi government abolished April 2003, Saddam Hussein executed.
In many instances, the United States has engaged in extended military engagements that were authorized by United Nations Security Council Resolutions and funded by appropriations from Congress.
|Military engagement||Opponent(s)||Initial authorization||President||Result|
|Korean War|| China
||UNSCR 84, 1950||Harry S. Truman||Korean Armistice Agreement, 1953|
|Multinational Force in Lebanon||Shia militias, Druze militias, Syria||UNSCR 425, 1978
UNSCR 426, 1978
|Jimmy Carter, Ronald Reagan||U.S. forces withdrew in 1984|
|Persian Gulf War||Iraq||UNSCR 678, 1990||George H. W. Bush||UNSCR 689, 1991|
|Bosnian War||Republika Srpska||UNSCR 770, 1992
UNSCR 776, 1992
UNSCR 836, 1993
|Bill Clinton||Reflagged as IFOR in 1995, Reflagged as SFOR in 1996, Completed in 2004|
|Second Liberian Civil War||Peacekeeping||UNSCR 1497, 2003||George W. Bush||U.S. forces are withdrawn in 2003 after the UNMIL is established.|
|Haitian coup d'état||UNSCR 1529, 2004
UNSCR 1542, 2004
|First Libyan Civil War||Libya||UNSCR 1973, 2011||Barack Obama||Debellation of the Libyan Arab Jamahiriya, October 31, 2011|
On at least 125 occasions, the President has acted without prior express military authorization from Congress. These include instances in which the United States fought in the Philippine–American War from 1898–1903, in Nicaragua in 1927, as well as the NATO bombing campaign of Yugoslavia in 1999, and the 2018 missile strikes on Syria.
The United States' longest war, against the Taliban in Afghanistan, began in 2001 and ended with the withdrawal of American troops on 31 August 2021.
The Indian Wars comprise at least 28 conflicts and engagements. These localized conflicts, with Native Americans, began with European colonists coming to North America, long before the establishment of the United States. For the purpose of this discussion, the Indian Wars are defined as conflicts with the United States of America. They begin as one front in the American Revolutionary War in 1775 and had concluded by 1918. The United States Army still maintains a campaign streamer for Pine Ridge 1890–1891 despite opposition from certain Native American groups.
The American Civil War was not an international conflict under the laws of war, because the Confederate States of America (CSA) was not a government that had been granted full diplomatic recognition as a sovereign nation by other sovereign states or by the government of the United States.
Main article: War Powers Resolution
In 1973, following the withdrawal of most American troops from the Vietnam War, a debate emerged about the extent of presidential power in deploying troops without a declaration of war. A compromise in the debate was reached with the War Powers Resolution. This act clearly defined how many soldiers could be deployed by the President of the United States and for how long. It also required formal reports by the President to Congress regarding the status of such deployments, and limited the total amount of time that American forces could be deployed without a formal declaration of war.
Although the constitutionality of the act has never been tested, it is usually followed, most notably during the Grenada Conflict, the Panamanian Conflict, the Somalia Conflict, the Persian Gulf War, and the Iraq War[clarification needed]. The only exception was President Clinton's use of U.S. troops in the 78-day NATO air campaign against Yugoslavia during the Kosovo War. In all other cases, the President asserted the constitutional authority to commit troops without the necessity of congressional approval, but in each case the President received congressional authorization that satisfied the provisions of the War Powers Act.
On March 21, 2011, a number of lawmakers expressed concern that the decision of President Barack Obama to order the U.S. military to join in attacks of Libyan air defenses and government forces exceeded his constitutional authority because the decision to authorize the attack was made without congressional permission. Obama explained his rationale in a two-page letter, stating that as commander in chief, he had constitutional authority to authorize the strikes, which would be limited in scope and duration, and necessary to prevent a humanitarian disaster in Libya.
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The Confederate States did not constitute a new state and they were not independent, hence they were not entitled to treatment by the United States as a foreign state.