The following list reviews hundreds of instances in which the United States has used military forces abroad in situations of military conflict or potential conflict to protect U.S. citizens or promote U.S. interests. The list does not include covert actions or numerous occurrences in which U.S. forces have been stationed abroad since World War II in occupation forces or for participation in mutual security organizations, base agreements, or routine military assistance or training operations. Because of differing judgments over the actions to be included, other lists may include more or fewer instances. These cases vary greatly in size of operation, legal authorization, and significance. The number of troops involved ranges from a few sailors or marines landed to protect American lives and property to hundreds of thousands in Korea and Vietnam and millions in World War II. Some actions were of short duration, and some lasted a number of years. In some examples, a military officer acted without authorization; some actions were conducted solely under the President's powers as Chief Executive or Commander in Chief; other instances were authorized by Congress in some fashion. In 11 separate cases (listed in bold-face type ) the United States formally declared war against foreign nations. For most of the instances listed, however, the status of the action under domestic or international law has not been addressed. Most occurrences listed since 1980 are summaries of U.S. military deployments reported to Congress by the President as a result of the War Powers Resolution. Several of these presidential reports are summaries of activities related to an ongoing operation previously reported. Note that inclusion in this list does not connote either legality or level of significance of the instance described. This report covers uses of U.S. military force abroad from 1798 to December 2018. It will be revised as circumstances warrant. CRS In Focus IF10675, Army Security Force Assistance Brigades (SFABs) , by Andrew Feickert. CRS In Focus IF10534, Defense Primer: President's Constitutional Authority with Regard to the Armed Forces , by Jennifer K. Elsea. CRS In Focus IF10535, Defense Primer: Congress's Constitutional Authority with Regard to the Armed Forces , by Jennifer K. Elsea. CRS In Focus IF10539, Defense Primer: Legal Authorities for the Use of Military Forces , by Jennifer K. Elsea. CRS In Focus IF10165, South Korea: Background and U.S. Relations , by Mark E. Manyin, Emma Chanlett-Avery, and Brock R. Williams. CRS Insight IN10797, Attack on U.S. Soldiers in Niger: Context and Issues for Congress , by Alexis Arieff. CRS Report R44853, Additional Troops for Afghanistan? Considerations for Congress , by Kathleen J. McInnis and Andrew Feickert. CRS Report RL30588, Afghanistan: Post-Taliban Governance, Security, and U.S. Policy , by Kenneth Katzman. CRS Report R43344, Conflict in South Sudan and the Challenges Ahead , by Lauren Ploch Blanchard. CRS Report R41989, Congressional Authority to Limit Military Operations , by Jennifer K. Elsea, Michael John Garcia, and Thomas J. Nicola. CRS Report R43377, The Central African Republic: Background and U.S. Policy , by Alexis Arieff and Tomas F. Husted. CRS Report RL31133, Declarations of War and Authorizations for the Use of Military Force: Historical Background and Legal Implications , by Jennifer K. Elsea and Matthew C. Weed. CRS Report R42699, The War Powers Resolution: Concepts and Practice , by Matthew C. Weed. CRS Report R43612, The Islamic State and U.S. Policy , by Christopher M. Blanchard and Carla E. Humud. CRS Report R43478, NATO: Response to the Crisis in Ukraine and Security Concerns in Central and Eastern Europe , coordinated by Paul Belkin. CRS Report RL33460, Ukraine: Current Issues and U.S. Policy , by Vincent L. Morelli. CRS Report R41481, U.S.-South Korea Relations , coordinated by Mark E. Manyin. CRS Report R42077, The Unified Command Plan and Combatant Commands: Background and Issues for Congress , by Andrew Feickert. CRS Report RS21405, U.S. Periods of War and Dates of Recent Conflicts , by Barbara Salazar Torreon. In addition to the historical resources listed in the " Introduction ," below are official government websites that serve as authoritative sources of information for this report. Central Intelligence Agency (CIA), News & Information, Press Releases and Statements https://www.cia.gov/news-information/press-releases-statements Department of Defense (DOD), News Releases https://dod.defense.gov/News/Releases/ DOD, Secretary of Defense Speeches https://dod.defense.gov/News/Speeches/SECDEF-All-Speeches/ DOD, Transcripts https://dod.defense.gov/News/Transcripts/ DOD, America's Continued Commitment to European Security, Operation Atlantic Resolve https://dod.defense.gov/News/Special-Reports/0218_Atlantic-Resolve/ DOD, Operation Inherent Resolve (OIR), Targeted Operations to Defeat ISIS https://dod.defense.gov/OIR/ DOD, Unified Command Plan, Commanders' Area of Responsibility https://www.defense.gov/know-your-military/combatant-commands/ Department of the Army, Official Army Announcements https://www.army.mil/news/newsreleases Department of the Navy, Continuing Promise Humanitarian Missions http://www.navy.mil/local/cp/index.asp Department of State, Bureau of Public Affairs: Office of Press Relations http://www.state.gov/r/pa/prs/ The White House Briefing Room , Briefings and Statements https://www.whitehouse.gov/briefings-statements/

Summary:
This report lists hundreds of instances in which the United States has used its Armed Forces abroad in situations of military conflict or potential conflict or for other than normal peacetime purposes. It was compiled in part from various older lists and is intended primarily to provide a rough survey of past U.S. military ventures abroad, without reference to the magnitude of the given instance noted. The listing often contains references, especially from 1980 forward, to continuing military deployments, especially U.S. military participation in multinational operations associated with NATO or the United Nations. Most of these post-1980 instances are summaries based on presidential reports to Congress related to the War Powers Resolution. A comprehensive commentary regarding any of the instances listed is not undertaken here. The instances differ greatly in number of forces, purpose, extent of hostilities, and legal authorization. Eleven times in its history, the United States has formally declared war against foreign nations. These 11 U.S. war declarations encompassed five separate wars: the war with Great Britain declared in 1812; the war with Mexico declared in 1846; the war with Spain declared in 1898; the First World War, during which the United States declared war with Germany and with Austria-Hungary during 1917; and World War II, during which the United States declared war against Japan, Germany, and Italy in 1941, and against Bulgaria, Hungary, and Rumania in 1942. Some of the instances were extended military engagements that might be considered undeclared wars. These include the Undeclared Naval War with France from 1798 to 1800; the First Barbary War from 1801 to 1805; the Second Barbary War of 1815; the Korean War of 1950-1953; the Vietnam War from 1964 to 1973; the Persian Gulf War of 1991; global actions against foreign terrorists after the September 11, 2001, attacks on the United States; and the war with Iraq in 2003. With the exception of the Korean War, all of these conflicts received congressional authorization in some form short of a formal declaration of war. Other, more recent instances have often involved deployment of U.S. military forces as part of a multinational operation associated with NATO or the United Nations. The majority of the instances listed prior to World War II were brief Marine Corps or Navy actions to protect U.S. citizens or promote U.S. interests. A number were engagements against pirates or bandits. Covert operations, domestic disaster relief, and routine alliance stationing and training exercises are not included here, nor are the Civil and Revolutionary Wars and the continual use of U.S. military units in the exploration, settlement, and pacification of the western part of the United States. For additional information, see CRS Report RL31133, Declarations of War and Authorizations for the Use of Military Force: Historical Background and Legal Implications, by Jennifer K. Elsea and Matthew C. Weed and CRS Report R41989, Congressional Authority to Limit Military Operations, by Jennifer K. Elsea, Michael John Garcia, and Thomas J. Nicola.