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 that an authorization suffices for declaration and that 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-aligned 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.
Tables
· Declarations of War › Formal Declarations of War
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Senate
Senate
War
Senate
Opponent
House
War of 1812
War of 1812
War
War of 1812
Opponent
United Kingdom
Declaration
United States declaration of war on the United Kingdom
Date
June 17, 1812
Votes
19–13
Votes
79–49
President
James Madison
Result
Treaty of Ghent
Mexican–American War
Mexican–American War
War
Mexican–American War
Opponent
Mexico
Declaration
United States declaration of war on Mexico
Date
May 13, 1846
Votes
40–2
Votes
174–14
President
James K. Polk
Result
Treaty of Guadalupe Hidalgo
Spanish–American War
Spanish–American War
War
Spanish–American War
Opponent
Spain
Declaration
United States declaration of war on Spain
Date
April 25, 1898
Votes
90-0
Votes
311–6
President
William McKinley
Result
Treaty of Paris (1898)
World War I
World War I
War
World War I
Opponent
Germany
Declaration
United States declaration of war on Germany (1917)
Date
April 6, 1917
Votes
82–6
Votes
373–50
President
Woodrow Wilson
Result
U.S.–German Peace Treaty (1921)
World War I
World War I
War
World War I
Opponent
Austria-Hungary
Declaration
United States declaration of war on Austria-Hungary
Date
December 7, 1917
Votes
74–0
Votes
350–1
President
Woodrow Wilson
Result
U.S.–Austrian Peace Treaty (1921)
World War II
World War II
War
World War II
Opponent
Japan
Declaration
United States declaration of war on Japan
Date
December 8, 1941
Votes
82–0
Votes
388–1
President
Franklin D. Roosevelt
Result
Treaty of San Francisco
World War II
World War II
War
World War II
Opponent
Germany
Declaration
United States declaration of war on Germany (1941)
Date
December 11, 1941
Votes
88–0
Votes
393–0
President
Franklin D. Roosevelt
Result
German Instrument of Surrender
World War II
World War II
War
World War II
Opponent
Italy
Declaration
United States declaration of war on Italy
Date
December 11, 1941
Votes
90–0
Votes
399–0
President
Franklin D. Roosevelt
Result
Treaty of Paris (1947)
World War II
World War II
War
World War II
Opponent
Bulgaria
Declaration
United States declaration of war on Bulgaria
Date
June 4, 1942
Votes
73–0
Votes
357–0
President
Franklin D. Roosevelt
Result
Treaties of Paris (1947)
World War II
World War II
War
World War II
Opponent
Hungary
Declaration
United States declaration of war on Hungary
Date
June 4, 1942
Votes
73–0
Votes
360–0
President
Franklin D. Roosevelt
Result
Treaties of Paris (1947)
World War II
World War II
War
World War II
Opponent
Romania
Declaration
United States declaration of war on Romania
Date
June 4, 1942
Votes
73–0
Votes
361–0
President
Franklin D. Roosevelt
Result
Treaties of Paris (1947)
Ranked list
War
Opponent
Declaration
Date
Votes
President
Result
Senate
House
War of 1812
United Kingdom
United States declaration of war on the United Kingdom
June 17, 1812
19–13
79–49
James Madison
Treaty of Ghent
Mexican–American War
Mexico
United States declaration of war on Mexico
May 13, 1846
40–2
174–14
James K. Polk
Treaty of Guadalupe Hidalgo
Spanish–American War
Spain
United States declaration of war on Spain
April 25, 1898
90-0
311–6
William McKinley
Treaty of Paris (1898)
World War I
Germany
United States declaration of war on Germany (1917)
April 6, 1917
82–6
373–50
Woodrow Wilson
German Peace Treaty (1921)
World War I
Austria-Hungary
United States declaration of war on Austria-Hungary
December 7, 1917
74–0
350–1
Woodrow Wilson
Austrian Peace Treaty (1921)
World War II
Japan
United States declaration of war on Japan
December 8, 1941
82–0
388–1
Franklin D. Roosevelt
Treaty of San Francisco
World War II
Germany
United States declaration of war on Germany (1941)
December 11, 1941
88–0
393–0
Franklin D. Roosevelt
German Instrument of Surrender
World War II
Italy
United States declaration of war on Italy
December 11, 1941
90–0
399–0
Franklin D. Roosevelt
Treaty of Paris (1947)
World War II
Bulgaria
United States declaration of war on Bulgaria
June 4, 1942
73–0
357–0
Franklin D. Roosevelt
Treaties of Paris (1947)
World War II
Hungary
United States declaration of war on Hungary
June 4, 1942
73–0
360–0
Franklin D. Roosevelt
Treaties of Paris (1947)
World War II
Romania
United States declaration of war on Romania
June 4, 1942
73–0
361–0
Franklin D. Roosevelt
Treaties of Paris (1947)
· Undeclared wars › Military engagements authorized by Congress
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Senate
Senate
War or conflict
Senate
Opponent(s)
House
Quasi-War
Quasi-War
War or conflict
Quasi-War
Opponent(s)
France
Initial authorization
An Act further to protect the commerce of the United StatesJuly 9, 1798
Votes
18–4
President
John Adams
Details of Authorization
Adams requested legislation allowing the United States Navy to defend American shipping after repeated attacks by the French Navy during the French Revolutionary Wars.
Result
Treaty of Mortefontaine
First Barbary War
First Barbary War
War or conflict
First Barbary War
Opponent(s)
Morocco
Tripolitania
Initial authorization
"An Act for the Protection of the Commerce and Seamen of the United States, Against the Tripolitan Cruisers", 2 Stat. 129, February 6, 1802
President
Thomas Jefferson
Details of Authorization
President Jefferson requested legislation allowing the U. S. Navy to defend shipping in the Mediterranean Sea from Tripolitanian vessels.
Result
War ended 1805
Second Barbary War
Second Barbary War
War or conflict
Second Barbary War
Opponent(s)
Algiers
Initial authorization
"An Act for the protection of the commerce of the United States against the Algerine cruisers", 3 Stat. 230, May 10, 1815
President
James Madison
Details of Authorization
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.
Result
War ended 1816
Enforcing 1808 slave trade ban; naval squadron sent to African waters to apprehend illegal slave traders
Enforcing 1808 slave trade ban; naval squadron sent to African waters to apprehend illegal slave traders
War or conflict
Enforcing 1808 slave trade ban; naval squadron sent to African waters to apprehend illegal slave traders
Opponent(s)
Slave traders
Initial authorization
"Act in addition to the acts prohibiting the Slave Trade", 3 Stat. 532, 1819
President
James Monroe
Result
1822 first African-American settlement founded in Liberia, 1823 U.S. Navy stops anti-trafficking patrols
Suppression of Piracy
Suppression of Piracy
War or conflict
Suppression of Piracy
Opponent(s)
Pirates
Initial authorization
1819
President
James Monroe
Details of Authorization
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
Redress for attack on U.S. Navy's USS Water Witch
War or conflict
Redress for attack on U.S. Navy's USS Water Witch
Opponent(s)
Paraguay
Initial authorization
1858.
President
James Buchanan
Mexican Revolution
United States occupation of Veracruz
Mexican Revolution
United States occupation of Veracruz
War or conflict
Mexican Revolution
United States occupation of Veracruz
Opponent(s)
Mexico
Initial authorization
H.J.R. 251, 38 Stat. 770April 22, 1914
Votes
337–37
President
Woodrow Wilson
Result
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
Allied intervention in the Russian Civil War
Russian Civil War
Allied intervention in the Russian Civil War
War or conflict
Russian Civil War
Allied intervention in the Russian Civil War
Opponent(s)
Commune of Estonia
Far Eastern Republic
Latvia
Mongolian People's Party
Russia
Ukraine
Initial authorization
1918
President
Woodrow Wilson
Lebanon crisis of 1958
Lebanon crisis of 1958
War or conflict
Lebanon crisis of 1958
Opponent(s)
Lebanese Opposition
Al-Mourabitoun
Lebanese Communist Party
Progressive Socialist Party
Initial authorization
H.J. Res. 117, Public Law 85-7, Joint Resolution "To promote peace and stability in the Middle East", March 9, 1957
Votes
72–19
Votes
355–61
President
Dwight D. Eisenhower
Details of Authorization
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.
Result
U.S. forces withdrawn, October 25, 1958
Vietnam War
Laotian Civil War
Cambodian Civil War
Vietnam War
Laotian Civil War
Cambodian Civil War
War or conflict
Vietnam War
Laotian Civil War
Cambodian Civil War
Opponent(s)
Mainland China
National United Front of Kampuchea
Khmer Rouge
Khmer Rumdo
Khmer Việt Minh
North Korea
North Vietnam
Pathet Lao
South Vietnam
Việt Cộng
Initial authorization
Gulf of Tonkin Resolution, August 7, 1964
Votes
88–2
Votes
416–0
President
Lyndon B. Johnson
Details of Authorization
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.
Result
U.S. forces withdrawn under terms of the Paris Peace Accords signed January 27, 1973
Multinational Force in Lebanon
Multinational Force in Lebanon
War or conflict
Multinational Force in Lebanon
Opponent(s)
Shia militias, Druze militias, Syria
Initial authorization
S.J.Res. 159Pub. L. 98–119September 29, 1983
Votes
54–46
Votes
253–156
President
Ronald W. Reagan
Details of Authorization
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.
Ranked list
War or conflict
Opponent(s)
Initial authorization
Votes
President
Details of Authorization
Result
Senate
House
Quasi-War
France
An Act further to protect the commerce of the United StatesJuly 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 Tripolitania
"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
Algiers
"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 United States occupation of Veracruz
Mexico
Stat. 770April 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 Allied intervention in the Russian Civil War
Commune of Estonia Far Eastern Republic Latvia Mongolian People's Party Russia Ukraine
1918
Woodrow Wilson
Lebanon crisis of 1958
Lebanese Opposition Al-Mourabitoun Lebanese Communist Party Progressive Socialist Party
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.
forces withdrawn, October 25, 1958
Vietnam War Laotian Civil War Cambodian Civil War
Mainland China National United Front of Kampuchea Khmer Rouge Khmer Rumdo Khmer Việt Minh North Korea North Vietnam Pathet Lao South Vietnam Việt Cộng
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.
forces withdrawn under terms of the Paris Peace Accords signed January 27, 1973
Multinational Force in Lebanon
Shia militias, Druze militias, Syria
Res. 159Pub. L. 98–119September 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
Res. 77January 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 Quetta Shura Taliban Haqqani network Mullah Dadullah Front al-Qaeda 055 Brigade Al-Nusra Front Khorasan group al-Qaeda Emirate in Yemen Aden-Abyan Islamic Army Islamic Jihad of Yemen al-Qaeda in the Arabian Peninsula Ansar al-Sharia al-Qaeda in the Indian Subcontinent Lashkar al-Zil Harakat Ahrar al-Sham al-Islamiyya Hezb-e Islami Gulbuddin Islamic Jihad Union Islamic Movement of Uzbekistan Jamaat-ul-Ahrar Jundallah Lashkar-e-Islam Lashkar-e-Jhangvi Tehreek-e-Nafaz-e-Shariat-e-Mohammadi Turkistan Islamic Party Tehrik-i-Taliban Pakistan High Council of the Islamic Emirate Fidai Mahaz al-Itihaad al-Islamiya Alliance for the Re-liberation of Somalia Harakat al-Shabaab Mujahedeen Hizbul Islam Islamic Courts Union Jabhatul Islamiya Mu'askar Anole Ras Kamboni Brigades Abu Sayyaf Bangsamoro Islamic Freedom Fighters Islamic State Islamic Movement of Uzbekistan Maute group Khalifa Islamiyah Mindanao
Res. 23September 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. The United States House of Representatives voted to repeal the 2001 AUMF in 2021.
Iraq War
Ba'athist Iraq
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. War ended December 15, 2011. Destabilization of Iraq and emergence of ISIL (ISIS) in Iraq region 2014–2017. During the 2019–2021 Persian Gulf crisis, President Donald Trump cited the AUMF in its assassination of Qasem Soleimani. The United States House of Representatives voted to repeal the AUMF in 2021.
· Undeclared wars › Military engagements authorized by United Nations Security Council Resolutions and funded by Congress
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Korean War
Korean War
Military engagement
Korean War
Opponent(s)
China North Korea Soviet Union
Initial authorization
UNSCR 84, 1950
President
Harry S. Truman
Result
Korean Armistice Agreement, 1953
Multinational Force in Lebanon
Multinational Force in Lebanon
Military engagement
Multinational Force in Lebanon
Opponent(s)
Shia militias, Druze militias, Syria
Initial authorization
UNSCR 425, 1978
UNSCR 426, 1978
President
Jimmy Carter, Ronald Reagan
Result
U.S. forces withdrew in 1984
Persian Gulf War
Persian Gulf War
Military engagement
Persian Gulf War
Opponent(s)
Iraq
Initial authorization
UNSCR 678, 1990
President
George H. W. Bush
Result
UNSCR 689, 1991
Bosnian War
Bosnian War
Military engagement
Bosnian War
Opponent(s)
Republika Srpska
Initial authorization
UNSCR 770, 1992UNSCR 776, 1992UNSCR 836, 1993
President
Bill Clinton
Result
Reflagged as IFOR in 1995, Reflagged as SFOR in 1996, Completed in 2004
Second Liberian Civil War
Second Liberian Civil War
Military engagement
Second Liberian Civil War
Opponent(s)
N/A
(Peacekeeping)
Initial authorization
UNSCR 1497, 2003
President
George W. Bush
Result
U.S. forces are withdrawn in 2003 after the UNMIL is established.
Haitian coup d'état
Haitian coup d'état
Military engagement
Haitian coup d'état
Opponent(s)
UNSCR 1529, 2004
UNSCR 1542, 2004
Initial authorization
2004
First Libyan Civil War
2011 military intervention in Libya
Operation Odyssey Dawn
Operation Unified Protector
First Libyan Civil War
2011 military intervention in Libya
Operation Odyssey Dawn
Operation Unified Protector
Military engagement
First Libyan Civil War
2011 military intervention in Libya
Operation Odyssey Dawn
Operation Unified Protector
Opponent(s)
Libya
Initial authorization
UNSCR 1973, 2011
President
Barack Obama
Result
Debellation of the Libyan Arab Jamahiriya, October 31, 2011
Ranked list
Military engagement
Opponent(s)
Initial authorization
President
Result
Korean War
China North Korea Soviet Union
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
forces withdrew in 1984
Persian Gulf War
Iraq
UNSCR 678, 1990
George H. W. Bush
UNSCR 689, 1991
Bosnian War
Republika Srpska
UNSCR 770, 1992UNSCR 776, 1992UNSCR 836, 1993
Bill Clinton
Reflagged as IFOR in 1995, Reflagged as SFOR in 1996, Completed in 2004
Second Liberian Civil War
N/A (Peacekeeping)
UNSCR 1497, 2003
George W. Bush
forces are withdrawn in 2003 after the UNMIL is established.
Haitian coup d'état
UNSCR 1529, 2004 UNSCR 1542, 2004
2004
First Libyan Civil War 2011 military intervention in Libya Operation Odyssey Dawn Operation Unified Protector
Libya
UNSCR 1973, 2011
Barack Obama
Debellation of the Libyan Arab Jamahiriya, October 31, 2011
