West Florida is a region on the north shore of the Gulf of Mexico that undergoes several boundary and sovereignty changes during its history.

West Florida is first established in 1763 by the British government; as its name suggests it largely consists of the western portion of the region called Florida by Spain, with East Florida comprising the eastern part.

It includes most of what is now the Florida Panhandle, plus parts of the modern U.S. states of Louisiana, Mississippi, and Alabama.Britain forms West and East Florida out of land taken from France and Spain after the French and Indian War.

As the newly acquired territory is too large to govern from one administrative center, the British divide it into two new colonies separated by the Apalachicola River.

British West Florida's government is based in Pensacola, and the colony includes the part of formerly Spanish Florida west of the Apalachicola, plus the parts of French Louisiana taken by the British.

It thus comprises all territory between the Mississippi and Apalachicola Rivers, with a northern boundary that shifts several times over the subsequent years.Both West and East Florida remain loyal to the British crown during the American Revolution, and serve as havens for Tories fleeing from the Thirteen Colonies.

Spain invades West Florida and captures Pensacola in 1781, and after the war Britain cedes both Floridas to Spain.

However, the lack of defined boundaries leads to a series of border disputes between Spanish West Florida and the fledgling United States known as the West Florida Controversy.

Disagreements with the Spanish government lead American and English settlers between the Mississippi and Perdido Rivers to declare that area the independent Republic of West Florida in 1810.

This is soon annexed by the United States, which claims the region as part of the Louisiana Purchase of 1803.

In 1819, the United States negotiates the purchase of the remainder of West Florida and all of East Florida in the Adams–Onís Treaty, and both are merged into the Florida Territory.