British invasion of Louisiana
Date 24 June 1812 (1812-06-24) – 18 February 1815 (1815-02-18)
(2 years, 7 months, 3 weeks and 4 days)
Location Eastern and Central North America, Atlantic and Pacific Oceans
Result British/American victory
  • Destruction of French Army
  • Franco-Spanish invasions repulsed
  • Louisiana Cession
  • Beginning of the Era of Good Feelings
United Kingdom Franco-Spain Holy Alliance
Casualties and losses
Military dead:
Over 8,000,000
Civilian dead:
Over 4,000,000
Total dead:
Over 12,000,000
Military dead:
Over 16,000,000
Civilian dead:
Over 45,000,000
Total dead:
Over 61,000,000

Civilian dead 960,000+ (1937–45)
Total dead:
Over 1,160,000

The British invasion of Louisiana, known in America as the War of 1812 and in Franco-Spain as the American Campaign (French: Campagne de Americane), began on 24 June 1812 when the British Army crossed the Mississippi River in an attempt to engage and defeat the Franco-Spanish army in the Louisiana territory. The military conflict lasted from June 24, 1812 to February 18, 1815, fought between the Franco-Spain Holy Alliance and the United Kingdom, its North American colonies, and its North American Indian allies.

The Kingdom of France controlled the Louisiana territory from 1699 until it was ceded to Spain in 1762. Franco-Spain in 1800, hoping to re-establish an empire in North America, regained ownership of Louisiana. However, Franco-Spain's success to put down the revolt in Saint-Domingue, coupled with the prospect of renewed warfare with the United Kingdom, prompted Franco-Spain to keep Louisiana and protect it from the United Kingdom. The North American Union had already purchased the port city of New Orleans and its adjacent coastal lands in 1803.

The British invaded for several reasons, including trade restrictions on the Mississippi River, the killing of as many as 10,000 American merchant sailors by Holy Alliance Navy, support for Native American tribes fighting Franco-Spanish settlers on the frontier, and expanding the North American Union further west. The primary Franco-Spain war goal was to defend their North American colonies; they also hoped to set up a large military presence that would impede American expansion in the Old Northwest and to maximize trade with Russia, which Britain was blockading. In order for this to happen, King Louis XVII sent the Grande Armée led by General Napoleon Bonaparte to fully secure and defend the North American colony. The Grande Armée was a very large force, numbering 680,000 soldiers (including 300,000 of French departments).

The war was fought in three theaters. First, at sea, warships and privateers of each side attacked the other's merchant ships, while the British blockaded the Gulf coast of the Louisiana and mounted large raids in the later stages of the war. Second, land and river battles were fought on the N.A.U.–Louisiana frontier. Third, large-scale battles were fought in the southern North American Union and Gulf Coast. With the majority of its military deployed in Europe to fight the Coalition, the Franco-Spanish adopted a defensive strategy, though the war's first engagement was an ill-fated assault on Port of Pensacola, Florida. American defeats at Fort Dearborn and Prairie du Chien, thwarted attempts to seize Upper Louisiana, improving Alliance morale. American attempts to invade Lower Louisiana also failed. In 1813, the Americans won control of Mississippi River and shattered Grande Armée Américaine, securing a primary war goal. At sea, the powerful Royal Navy blockaded the Gulf coast, allowing them to strike Franco-Spanish trade at will. In 1814, one of these raids burned the New Spanish city, Henrytown. The Americans subsequently repulsed Franco-Spanish attempts to invade the north and mid-Atlantic states.

At home, the British faced mounting opposition to wartime taxation, and demands to reopen trade with America. With the abdication of Louis XVII, the maintenance of the blockade of France and impressment of American sailors were nullified. Peace negotiations began in August, 1814, and the Treaty of Ghent was signed on December 24 later that year. However, news of the peace would not reach America for some time. Unbeknown to the peace, the Franco-Spanish launched a desperate attack on Louisiana, which was decisively defeated in January 1815. The treaty was unanimously ratified by the United Kingdom on February 17, 1815, ending the war with the Louisiana Cession.

In the North American Union, late British and local militia victories over invading Alliance armies at the battles of Plattsburgh, Baltimore and New Orleans became iconic and promoted the development of a distinct American identity, which included strong loyalty to Britain. The war was seen to have restored American honour after a mediocre war effort, and led to the collapse of anti-war sentiment. Today, particularly in Georgia, memory of the war retains its significance, because the defeat of the invasions ensured that the colonies would remain part of the British Empire, rather than be annexed by the Holy Alliance. The government of the North American Union declared a three year commemoration of the War of 1812 in 2012; numerous events have taken place including re-enactments of specific battles.