Spanish minister Do Luis de Onis and U.S. Secretary of State John Quincy Adams sign the Florida Purchase Treaty, in which Spain agrees to cede the remainder of its old province of Florida to the United States.
Spanish colonization of the Florida peninsula began at St. Augustine in 1565. The Spanish colonists enjoyed a brief period of relative stability before Florida came under attack from resentful Native Americans and ambitious English colonists to the north in the 17th century. Spain's last-minute entry into the French and Indian War on the side of France cost it Florida, which the British acquired through the first Treaty of Paris in 1763. After 20 years of British rule, however, Florida was returned to Spain as part of the second Treaty of Paris, which ended the American Revolution in 1783.
Spain's hold on Florida was tenuous in the years after American independence, and numerous boundary disputes developed with the United States. In 1819, after years of negotiations, Secretary of State John Quincy Adams achieved a diplomatic coup with the signing of the Florida Purchase Treaty, which officially put Florida into U.S. hands at no cost beyond the U.S. assumption of some $5 million of claims by U.S. citizens against Spain. Formal U.S. occupation began in 1821, and General Andrew Jackson, the hero of the War of 1812, was appointed military governor. Florida was organized as a U.S. territory in 1822 and was admitted into the Union as a slave state in 1845.