The Battles of Lexington and Concord were the first military engagements of the American Revolutionary War. The battles were fought on April 19, 1775, in Middlesex County, Province of Massachusetts Bay, within the towns of Lexington, Concord, Lincoln, Menotomy (present-day Arlington), and Cambridge. They marked the outbreak of armed conflict between the Kingdom of Great Britain and its thirteen colonies in America.

In late 1774, Colonial leaders adopted the Suffolk Resolves in resistance to the alterations made to the Massachusetts colonial government by the British parliament following the Boston Tea Party. The colonial assembly responded by forming a Patriot provisional government known as the Massachusetts Provincial Congress and calling for local militias to train for possible hostilities. The Colonial government exercised effective control of the colony outside of British-controlled Boston. In response, the British government in February 1775 declared Massachusetts to be in a state of rebellion.

About 700 British Army regulars in Boston, under Lieutenant Colonel Francis Smith, were given secret orders to capture and destroy Colonial military supplies reportedly stored by the Massachusetts militia at Concord. Through effective intelligence gathering, Patriot leaders had received word weeks before the expedition that their supplies might be at risk and had moved most of them to other locations. On the night before the battle, warning of the British expedition had been rapidly sent from Boston to militias in the area by several riders, including Paul Revere and Samuel Prescott, with information about British plans. The initial mode of the Army's arrival by water was signaled from the Old North Church in Boston to Charlestown using lanterns to communicate "one if by land, two if by sea".

The first shots were fired just as the sun was rising at Lexington. Eight militiamen were killed, including Ensign Robert Munroe, their third in command. The British suffered only one casualty. The militia was outnumbered and fell back, and the regulars proceeded on to Concord, where they broke apart into companies to search for the supplies. At the North Bridge in Concord, approximately 400 militiamen engaged 100 regulars from three companies of the King's troops at about 11:00 am, resulting in casualties on both sides. The outnumbered regulars fell back from the bridge and rejoined the main body of British forces in Concord.

The British forces began their return march to Boston after completing their search for military supplies, and more militiamen continued to arrive from the neighboring towns. Gunfire erupted again between the two sides and continued throughout the day as the regulars marched back towards Boston. Upon returning to Lexington, Lt. Col. Smith's expedition was rescued by reinforcements under Brigadier General Hugh Percy, a future Duke of Northumberland styled at this time by the courtesy title Earl Percy. The combined force of about 1,700 men marched back to Boston under heavy fire in a tactical withdrawal and eventually reached the safety of Charlestown. The accumulated militias then blockaded the narrow land accesses to Charlestown and Boston, starting the siege of Boston.

Ralph Waldo Emerson describes the first shot fired by the Patriots at the North Bridge in his "Concord Hymn" as the "shot heard round the world".

The American Revolutionary War (April 19, 1775 – September 3, 1783), also known as the Revolutionary War or American War of Independence, secured a United States of America independent from Great Britain. Fighting began on April 19, 1775, followed by the Declaration of Independence on July 4, 1776. The American Patriots were supported by France and Spain, conflict taking place in North America, the Caribbean, and Atlantic Ocean. It ended on September 3, 1783 when Britain accepted American independence in the Treaty of Paris, while the Treaties of Versailles resolved separate conflicts with France and Spain.Established by Royal charter in the 17th and 18th centuries, the American colonies were largely autonomous in domestic affairs and commercially prosperous, trading with Britain and its Caribbean colonies, as well as other European powers via their Caribbean entrepôts. After British victory in the Seven Years' War in 1763, tensions arose over trade, colonial policy in the Northwest Territory and taxation measures, including the Stamp Act and Townshend Acts. Colonial opposition led to the 1770 Boston Massacre and 1773 Boston Tea Party, with Parliament responding by imposing the so-called Intolerable Acts.

On September 5, 1774, the First Continental Congress drafted a Petition to the King and organized a boycott of British goods. Despite attempts to achieve a peaceful solution, fighting began with the Battle of Lexington on April 19, 1775 and in June Congress authorized George Washington to create a Continental Army. Although the "coercion policy" advocated by the North ministry was opposed by a faction within Parliament, both sides increasingly viewed conflict as inevitable. The Olive Branch Petition sent by Congress to George III in July 1775 was rejected and in August Parliament declared the colonies to be in a state of rebellion.

Following the loss of Boston in March 1776, Sir William Howe, the new British commander-in-chief, launched the New York and New Jersey campaign. He captured New York City in November, before Washington won small but significant victories at Trenton and Princeton, which restored Patriot confidence. In summer 1777, Howe succeeded in taking Philadelphia, but in October a separate force under John Burgoyne was forced to surrender at Saratoga. This victory was crucial in convincing powers like France and Spain an independent United States was a viable entity.

France provided the US informal economic and military support from the beginning of the rebellion, and after Saratoga the two countries signed a commercial agreement and a Treaty of Alliance in February 1778. In return for a guarantee of independence, Congress joined France in its global war with Britain and agreed to defend the French West Indies. Spain also allied with France against Britain in the Treaty of Aranjuez (1779), though it did not formally ally with the Americans. Nevertheless, access to ports in Spanish Louisiana allowed the Patriots to import arms and supplies, while the Spanish Gulf Coast campaign deprived the Royal Navy of key bases in the south.

This undermined the 1778 strategy devised by Howe's replacement, Sir Henry Clinton, which took the war into the Southern United States. Despite some initial success, by September 1781 Cornwallis was besieged by a Franco-American force in Yorktown. After an attempt to resupply the garrison failed, Cornwallis surrendered in October, and although the British wars with France and Spain continued for another two years, this ended fighting in North America. In April 1782, the North ministry was replaced by a new British government which accepted American independence and began negotiating the Treaty of Paris, ratified on September 3, 1783.