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The 1700s

JUNE 14, 1775

The Continental Congress authorizes the creation of the Continental Army, and the next day, puts it under the command of George Washington. After the Revolution, it would be known as the U.S. Army.

OCTOBER 13, 1775

The Continental Congress votes to create the Continental Navy, which later becomes the U.S. Navy.

NOVEMBER 10, 1775

The Second Continental Congress establishes the Continental Marines, predecessor of the U.S. Marine Corps.

JULY 4, 1776

The Second Continental Congress unanimously adopts the Declaration of Independence, announcing the colonies' separation from Britain.


American and British delegations sign Treaty of Paris, ending the Revolutionary War and recognizing the United States as an independent nation.

AUGUST 7, 1789

Congress establishes the War Department at the cabinet level to oversee the operation and maintenance of the Army, Navy and Marine Corps.

AUGUST 4, 1790

Congress Congress establishes the Revenue Cutter Service, predecessor of today's Coast Guard.

APRIL 30, 1798

The War Department transfers oversight of the Navy to the newly established Navy Department.

The 1800s

MARCH 16, 1802

President Thomas Jefferson signed the Military Peace Establishment Act into law, creating the U.S. Military Academy at West Point, N.Y.

JUNE 18, 1812

The United States declares war — what came to be known as the War of 1812 — on Great Britain in response to British naval blockades and the forced conscription of American sailors into the Royal Navy.

AUGUST 24, 1814

The War Department building is set on fire during the War of 1812. All books and records are saved, having been removed a few days earlier.

FEBRUARY 17, 1815

President James Madison ratifies the Treaty of Ghent, officially ending the War of 1812.

OCTOBER 10, 1845

The Naval School, a precursor to the Naval Academy, is established in Annapolis, Md.

MAY 13, 1846 -
MARCH 10, 1848

The United States and Mexico go to war over a border dispute in Texas and President James K. Polk's broader ambitions to claim Mexican territories in what are now the states of California and New Mexico.

JULY 1, 1850

The Naval School officially becomes known as the U.S. Naval Academy.

APRIL 12, 1861 -
APRIL 9, 1865

Civil War is fought between the United States and the Confederate States of America, the 11 southern states that left the Union after President Abraham Lincoln's election. After the war, the United States readmitted the former Confederate states and abolished the institution of slavery.


The War Department moves into the east wing of the new State-War-Navy Building, now known as the Eisenhower Executive Office Building.

APRIL 21 -
December 10, 1898

The United States goes to war with Spain in support of Cuban independence and in response to the sinking of the battleship USS Maine in Havana Harbor.

FEBRUARY 4, 1899 -
JULY 4, 1902

After the United States annexed the Philippines at the end of the Spanish-American War, Filipino revolutionaries wage an unsuccessful campaign for independence that lasts more than 3 years.

The 1900s

APRIL 6, 1917 -
NOVEMBER 11, 1918

The United States enters the war in Europe, joining the Allied Powers of France, Great Britain, Russia, Japan and Italy, against the Central Powers led by Germany and Austria-Hungary. The U.S. abandons neutrality nearly three years after the war began in response to German submarine attacks on American ships and attempts to disrupt diplomatic relations with the Mexican government.

July 2, 1926

The U.S. Army Air Corps is organized.

EARLY 1940s

The United States Army undergoes a sweeping reorganization to consolidate and optimize operating efficiencies vital to the war effort. Combat forces and logistics functions are grouped into three new field organizations: Army Ground Forces, Army Air Forces and Army Service Forces.

JULY 1941

Space constraints spurred the War Department, the Secretary of War and Congress to authorize the construction of the Pentagon. At that time, the War Department workforce in the Washington, D.C., area numbered more than 24,000 civilian and military personnel housed in 17 buildings and was expected to reach 30,000 by the beginning of 1942.

SEPTEMBER 11, 1941

Ground is broken on the Pentagon on land in Virginia, portions of which belonged to Confederate Gen. Robert E. Lee before the Civil War.

DECEMBER 7, 1941

Japan attacks Pearl Harbor and draws the United States into World War II. Two decades after “the war to end all wars,” World War II quickly becomes the deadliest conflict in world history.

JANUARY 15, 1943

The Pentagon officially opens, 16 months after construction began.

MAY 8, 1945

Germany surrenders, ending World War II in Europe.


Japan surrenders, officially ending World War II.

MARCH 12, 1947

President Harry Truman pledges U.S. support for democracies threatened by authoritarianism and urges congressional approval of economic and military assistance to thwart communist incursions in Greece and Turkey. This policy, known as the Truman Doctrine, helps set the stage for the Cold War rivalry between the United States and the Soviet Union.

JULY 26, 1947

President Harry Truman signs the National Security Act. The legislation merges the Navy and War Departments and the newly independent Air Force into a single organization called the National Military Establishment led by a civilian secretary of defense who also oversees the Joint Chiefs of Staff. In addition, the act creates the Central Intelligence Agency, the National Security Agency and the National Security Resources Board.

SEPTEMBER 17, 1947

The National Military Establishment begins operations under the direction of Secretary of Defense James V. Forrestal, who had stepped down as secretary of the Navy to serve in this new role.

SEPTEMBER 18, 1947

The U.S. Air Force is formally established.

AUGUST 10, 1949

The National Security Act is amended, renaming the National Military Establishment to the Department of Defense. The change rescinded the cabinet-level statuses of Army, Navy and Air Force secretaries and made them all subordinate to the secretary of defense, whose authority and responsibilities increased. The amendment also established a chairman for the Joint Chiefs of Staff.

AUGUST 16, 1949

Secretary of Defense Louis Johnson swears in famed World War II Army general Omar Bradley as the first chairman of the Joint Chiefs of Staff.

JUNE 25, 1950

The Korean War begins with the North Korean army’s invasion of South Korea. Through the United Nations Security Council, President Truman marshals international opposition to the invasion and, on June 27, 1950, commits air and naval forces to the defense of South Korea.

JULY 27, 1953

The Korean Armistice Agreement is signed, culminating in a cease fire that is still in force.

APRIL 1, 1954

The U.S. Air Force Academy is established at Colorado Springs, Colorado.

MARCH 8, 1965

The first U.S. combat troops arrive in South Vietnam.

MARCH 29, 1973

The last U.S. combat troops leave Vietnam, ending direct U.S. military involvement in the war.

JANUARY 17 - FEBRUARY 28, 1991

Operation Desert Storm is carried out against Iraq after it invades Kuwait, a major oil producer.

December 26, 1991

With the dissolution of the Soviet Union, the Cold War officially comes to an end.

The 2000s

SEPTEMBER 11, 2001

Al-Qaeda terrorists hijack 4 commercial airliners. Two hit the World Trade Center in New York City, one strikes the Pentagon in Washington, D.C., and the last jetliner crashes in an open field near the town of Shanksville in western Pennsylvania. The attacks claim 2,977 lives (building occupants and airline passengers).

OCTOBER 7, 2001

U.S. forces launch Operation Iraqi Freedom after Iraq refuses to comply with United Nations Security Council Resolution 1441, the last of several failed attempts short of war to prohibit Iraq from importing and stockpiling weapons of mass destruction.

MARCH 20, 2003

U.S. troops enter Iraq to begin Operation Iraqi Freedom after the country is found to have breached U.N. Security Council adopted Resolution 1441, which called on Iraq to cooperate unconditionally with U.N. weapons inspectors to verify that it was not in possession of weapons of mass destruction and ballistic missiles.

SEPTEMBER 11, 2008

The Defense Department honors those killed in the Sept. 11, 2001, terrorist attacks with the opening of the National 9/11 Pentagon Memorial.

DECEMBER 15, 2011

U.S. troops in Baghdad mark the official end of the mission in Iraq — renamed Operation New Dawn from Operation Iraqi Freedom in 2010 — ending nearly nine years of war.

AUGUST 8, 2014

Operation Inherent Resolve, a task force comprising U.S. military and coalition forces, begins to support Iraqi Security Force operations against the Islamic State of Iraq and Syria (ISIS).

December 31, 2014

U.S. combat operations in Afghanistan end; however, U.S. forces remain in the country to participate in Operation Freedom’s Sentinel, a coalition mission to train, advise and assist Afghan National Defense and Security Forces and to conduct counterterrorism operations against the remnants of al-Qaeda.

December 20, 2019

The U.S. Space Force is established as a separate military department in recognition of the growing need to strengthen defensive capabilities necessary to protect space-based economic and military assets.

AUGUST 30, 2021

U.S. forces withdraw from Afghanistan, airlifting more than 120,000 people to safety as the Taliban seizes control of the country.

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