East Florida was a colony of Great Britain from 1763 to 1783 and a province of Spanish Florida from 1783 to 1821. Great Britain gained control of the long-established Spanish colony of La Florida in 1763 as part of the treaty ending the French and Indian War . Deciding that the territory was too large to administer as a single unit, Britain divided Florida into two colonies separated by the Apalachicola River: East Florida with its capital in St. Augustine and West Florida with its capital in Pensacola. East Florida was much larger and comprised the bulk of the former Spanish territory of Florida and most of the current state of Florida. It had also been the most populated region of Spanish Florida, but before control was transferred to Britain, most residents – including virtually everyone in St. Augustine – left the territory, with most migrating to Cuba.