The Great Siege of Gibraltar was an unsuccessful attempt by Spain and France to capture Gibraltar from the British during the War of the American Revolution. It was the largest battle in the war by number of combatants. The American war had ended with the British defeat at Yorktown in October 1781, but the Bourbon defeat in their great final assault on Gibraltar would not come until September 1782. The siege was suspended in February 1783 at the beginning of peace talks with the British.On 16 June 1779, Spain entered the war on the side of France and as co-belligerents of the rebellious American coloniesthe British base at Gibraltar was Spain's primary war aim. The vulnerable Gibraltar garrison under George Augustus Eliott was blockaded from June 1779 to February 1783, initially by the Spanish alone, led by Martn lvarez de Sotomayor. The blockade proved to be a failure because two relief convoys entered unmolestedthe first under Admiral George Rodney in 1780 and the second under Admiral George Darby in 1781despite the presence of the Spanish fleets. The same year, a major assault was planned by the Spanish, but the Gibraltar garrison sortied in November and destroyed much of the forward batteries.

The Spanish having consistently failed to either defeat the garrison or prevent the arrival of relief efforts, the besiegers were reinforced by French forces under de Crillon, who took over command in early 1782. After a lull in the siege, during which the Franco-Spanish besiegers gathered more guns, ships and troops, a "Grand Assault" was launched on 18 September 1782. This involved huge numbers60,000 men, 49 ships of the line and 10 specially designed, newly invented floating batteriesagainst the 5,000 defenders. The assault proved to be a disastrous and humiliating failure, resulting in heavy losses for the Bourbon attackers. This was the largest action fought during the war in terms of numbers.

The final sign of defeat for the allies came when a crucial British relief convoy under Admiral Richard Howe slipped through the blockading fleet and arrived at the garrison in October 1782. The siege was finally lifted on 7 February 1783 and resulted in a decisive victory for the British. The siege was a factor in ending the American Revolutionary Warthe Peace of Paris negotiations were reliant on news from the siege, particularly at its climax.At three years, seven months and twelve days, it is the longest siege endured by the British Armed Forces.

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.