American Revolutionary War: Spain declares war on the Kingdom of Great Britain, and the Great Siege of Gibraltar begins.

The American Revolutionary War, also known as the Revolutionary War or American War of Independence, was the armed conflict that comprised the final eight years of the broader American Revolution, in which American Patriot forces organized as the Continental Army and commanded by George Washington defeated the British Army. The conflict was fought in North America, the Caribbean, and the Atlantic Ocean. The war's outcome seemed uncertain for most of the war. But Washington and the Continental Army's decisive victory in the Siege of Yorktown in 1781 led King George III and the Kingdom of Great Britain to negotiate an end to the war in the Treaty of Paris two years later, in 1783, in which the British monarchy acknowledged the independence of the Thirteen Colonies, leading to the establishment of the United States as an independent and sovereign nation.

Spain, through its alliance with France and as part of its conflict with Britain, played an important role in the independence of the United States. Spain declared war on Britain as an ally of France, itself an ally of the American colonies. Most notably, Spanish forces attacked British positions in the south and captured West Florida from Britain in the siege of Pensacola. This secured the southern route for supplies and closed off the possibility of any British offensive through the western frontier of the United States via the Mississippi River. Spain also provided money, supplies, and munitions to the American forces.

The Great Siege of Gibraltar was an unsuccessful attempt by Spain and France to capture Gibraltar from the British during the American Revolutionary War. It was the largest battle in the war by number of combatants.