American Revolutionary War: the Continental Army is established by the Continental Congress, marking the birth of the United States Army.

The United States Department of War first establishes a regular army with a strength of several hundred men.

Pike expedition: United States Army Lieutenant Zebulon Pike begins an expedition from Fort Bellefontaine near St. Louis, Missouri, to explore the west.

Osceola leads his Seminole warriors in Florida into the Second Seminole War against the United States Army.

American Old West: On the Sonoita River in present-day southern Arizona, the United States Army establishes Fort Buchanan in order to help control new land acquired in the Gadsden Purchase.

American Civil War: Baltimore riot of 1861, a pro-Secession mob in Baltimore, Maryland, attacks United States Army troops marching through the city.

American Civil War: Robert E. Lee resigns his commission in the United States Army in order to command the forces of the state of Virginia.

The United States Army abolishes flogging.

American Civil War: Citing failing health, Union General Winfield Scott resigns as Commander of the United States Army.

A group of Modoc warriors defeat the United States Army in the First Battle of the Stronghold, a part of the Modoc War.

Indian Wars: In retaliation for the American defeat at the Battle of the Little Bighorn, United States Army troops sack Chief Dull Knife's sleeping Cheyenne village at the headwaters of the Powder River.

Indian Wars: Sitting Bull leads his band of Lakota into Canada to avoid harassment by the United States Army under Colonel Nelson Miles.

U.S. Army aviation pioneer, Major Harold Geiger, dies in the crash of his Airco DH.4 de Havilland plane at Olmstead Field, Pennsylvania.

U.S. President Herbert Hoover orders the United States Army to forcibly evict the "Bonus Army" of World War I veterans gathered in Washington, D.C.

The United States Army Disciplinary Barracks on Alcatraz Island, is acquired by the United States Department of Justice

George C. Marshall becomes Chief of Staff of the United States Army.

Benjamin O. Davis Sr. is named the first African American general in the United States Army.

The United States Army contracts with the University of Pennsylvania's Moore School to develop the ENIAC.

World War II: During the Gilbert and Marshall Islands campaign, U.S. Army and Marine forces seize Kwajalein Atoll from the defending Japanese garrison.

World War II: The first Allied troops of the U.S. Army cross the western border of Germany.

US Army private Eddie Slovik is executed for desertion, the first such execution of an American soldier since the Civil War.

The United States Army liberates Nazi ''Sonderlager'' (high security) prisoner-of-war camp Oflag IV-C (better known as Colditz).

McCarthyism: Joseph Welch, special counsel for the United States Army, lashes out at Senator Joseph McCarthy during hearings on whether Communism has infiltrated the Army giving McCarthy the famous rebuke, "You've done enough. Have you no sense of decency, sir, at long last? Have you left no sense of decency?"

McCarthyism: Joseph Welch, special counsel for the United States Army, lashes out at Senator Joseph McCarthy during hearings on whether Communism has infiltrated the Army giving McCarthy the famous rebuke, "You've done enough. Have you no sense of decency, sir, at long last? Have you left no sense of decency?"

Central High School in Little Rock, Arkansas, is integrated by the use of United States Army troops.

The United States Army launches Explorer 1.

The United States Army launches Explorer 3.

President Dwight D. Eisenhower signs an executive order transferring Wernher von Braun and other German scientists from the United States Army to NASA.

United States occupation of the Dominican Republic: American troops land in the Dominican Republic to "forestall establishment of a Communist dictatorship" and to evacuate U.S. Army troops.

After refusing induction into the United States Army the day before (citing religious reasons), Muhammad Ali is stripped of his boxing title.

My Lai Massacre: The United States Army charges 14 officers with suppressing information related to the incident.

President Richard Nixon appoints Anna Mae Hays and Elizabeth P. Hoisington the first female United States Army Generals.

After being appointed on May 15, Anna Mae Hays and Elizabeth P. Hoisington officially receive their ranks as U.S. Army Generals, becoming the first females to do so.

Arrow Air Flight 1285 crashes after takeoff in Gander, Newfoundland killing 256, including 248 members of the United States Army's 101st Airborne Division.

A United States Air Force (USAF) F-16 aircraft collides with a USAF C-130 at Pope Air Force Base and then crashes, killing 24 United States Army soldiers on the ground. This later became known as the Green Ramp disaster.

In a U.S. friendly fire incident during Operation Provide Comfort in northern Iraq, two United States Air Force aircraft mistakenly shoot-down two United States Army helicopters, killing 26 people.

Two 14-year-old South Korean girls are struck and killed by a United States Army armored vehicle, leading to months of public protests against the US.

The United States Army veteran Terry Nichols is found guilty of 161 state murder charges for helping carry out the Oklahoma City bombing.

The last Mobile Army Surgical Hospital (MASH) is decommissioned by the United States Army.