The United States Army (U.S. Army) is the land service branch of the United States Armed Forces. It is designated as the army of the United States in the United States Constitution. As a part of the United States Department of Defense, it is one of the six armed forces of the United States and one of the eight uniformed services of the United States. Founded in 1784, it succeeded the Continental Army, formed in 1775 during the American Revolutionary War.
The U.S. Army is part of the Department of the Army, which is one of the three military departments of the Department of Defense. The Army is headed by the civilian secretary of the Army, and by the military chief of staff of the Army, a member of the Joint Chiefs of Staff. It is the largest military branch, and for FY2022, the projected headcount of the Army was 1,005,725 soldiers: the Regular Army 480,893 soldiers; the Army National Guard 336,129 soldiers, and the U.S. Army Reserve 188,703 soldiers. Major branches include Air Defense Artillery, Armor, Aviation, Field Artillery, Infantry, and Special Forces. With the world's highest vehicle-to-soldier ratio, the Army operates tens of thousands of combat vehicles, including the M1 Abrams main battle tank, Bradley armoured fighting vehicle, and UH-60 Black Hawk helicopters. The Army also deploys key systems for the Missile Defense Agency: the Ground-Based Midcourse Defense, Terminal High Altitude Area Defense, and MIM-104 Patriot.
The U.S. Army fought the American Indian Wars (1784–1890), the War of 1812 (1812–15), Mexican–American War (1846–48). The American Civil War (1861–65) was its costliest conflict, with over 350,000 casualties. It fought the Spanish–American War (1898), World War I (1917–18), World War II (1941–45). In the Cold War, the Army fought the Korean War (1950–53) and Vietnam War (1965–71), and operated tactical nuclear weapons ranging from the Pershing II ballistic missile to the Davy Crockett rifle. Following the Cold War's end in 1991, Army has focused primarily on Western Asia and counterinsurgency roles, including the Gulf War, war in Afghanistan, and war in Iraq. The U.S. Army currently conducts missiles strikes and defense in the 2026 Iran war, and provides materials and training to Ukraine in the Russo-Ukrainian war.
The United States Army serves as the primary land-based branch of the United States Department of Defense. Section 7062 of Title 10, U.S. Code defines the purpose of the army as:
Preserving the peace and security and providing for the defense of the United States, the Commonwealths and possessions, and any areas occupied by the United States
Supporting the national policies
Implementing the national objectives
Overcoming any nations responsible for aggressive acts that imperil the peace and security of the United States
In 2018, the Army Strategy 2018 articulated an eight-point addendum to the Army Vision for 2028. While the Army Mission remains constant, the Army Strategy builds upon the Army's Brigade Modernization by adding focus to corps and division-level echelons. The Army Futures Command oversees reforms geared toward conventional warfare. The Army's current reorganization plan is due to be completed by 2028.
The Army's five core competencies are prompt and sustained land combat, combined arms operations (to include combined arms maneuver and wide–area security, armored and mechanized operations and airborne and air assault operations), special operations forces, to set and sustain the theater for the joint force and to integrate national, multinational, and joint power on land.
The Continental Army was created on 14 June 1775 by the Second Continental Congress as a unified army for the colonies to fight Great Britain, with George Washington appointed as its commander. The army was initially led by men who had served in the British Army or colonial militias and who brought much of British military heritage with them. As the Revolutionary War progressed, French aid, resources, and military thinking helped shape the new army. A number of European soldiers came on their own to help, such as Friedrich Wilhelm von Steuben, who taught Prussian Army tactics and organizational skills.
The Army fought numerous pitched battles, and sometimes used Fabian strategy and hit-and-run tactics in the South in 1780 and 1781; under Major General Nathanael Greene, it hit where the British were weakest to wear down their forces. Washington led victories against the British at Trenton and Princeton, but lost a series of battles in the New York and New Jersey campaign in 1776 and the Philadelphia campaign in 1777. With a decisive victory at Yorktown and the help of the French, the Continental Army prevailed against the British.
After the war, the Continental Army was quickly given land certificates and disbanded in a reflection of the republican distrust of standing armies. State militias became the new nation's sole ground army, except a regiment to guard the Western Frontier and one battery of artillery guarding West Point's arsenal. However, because of continuing conflict with Native Americans, it was soon considered necessary to field a trained standing army. The Regular Army was at first very small and after General St. Clair's defeat at the Battle of the Wabash, where more than 800 soldiers were killed, the Regular Army was reorganized as the Legion of the United States, established in 1791 and renamed the United States Army in 1796.
In 1798, during the Quasi-War with France, the U.S. Congress established a three-year "Provisional Army" of 10,000 men, consisting of twelve regiments of infantry and six troops of light dragoons. In March 1799, Congress created an "Eventual Army" of 30,000 men, including three regiments of cavalry. Both "armies" existed only on paper, but equipment for 3,000 men and horses was procured and stored.
The War of 1812 was the second and last war between the United States and Great Britain. The war was split between a Northern, Southern, and naval campaign. While a large part of the war was fought between the United States and Great Britain, there were a variety of native tribes that fought on both sides of the conflict. The result of the war is the Treaty of Ghent and is generally considered to be inconclusive, and brought upon a period of peace between the United States and Great Britain that has lasted for over two centuries.
There was a long period of war between the United States and the Seminoles that lasted over 50 years. The usual strategies utilized against Native American tribes were to seize winter food supplies and to form alliances with enemies of a tribe. These were not viable options against the Seminoles, largely due to the fact of lack of climate variability in Florida and because of the long history of warring between the Seminole tribe and other tribes in the Florida region.
The U.S. Army fought and won the Mexican–American War, which was a defining event for both countries. The U.S. victory resulted in the Treaty of Guadalupe Hidalgo, in which Mexico ceded a large portion of land to the United States which included the modern-day states of California, Nevada, New Mexico, Arizona, Texas, and parts of Colorado and Wyoming.
The American Civil War was the costliest war for the U.S. in terms of casualties. After most slave states, located in the southern U.S., formed the Confederate States, the Confederate States Army, led by former U.S. Army officers, mobilized a large fraction of Southern white manpower. Forces of the United States (the "Union" or "the North") formed the Union Army, consisting of a small body of regular army units and a large body of volunteer units raised from every state, north and south, except South Carolina.