Florida
Florida had become a burden to Spain, which could not afford to send settlers or garrisons. Madrid therefore decided to cede the territory to the United States through the Adams–Onís Treaty, which took effect in 1821. President James Monroe was authorized on March 3, 1821 to take possession of East Florida and West Florida for the United States and provide for initial governance. Andrew Jackson, on behalf of the U.S. federal government, served as a military commissioner with the powers of governor of the newly acquired territory for a brief period. On March 30, 1822, the U.S. Congress merged East Florida and part of West Florida into the Florida Territory.
By the early 1800s, Indian removal was a significant issue throughout the southeastern U.S. and also in Florida. In 1830, the U.S. Congress passed the Indian Removal Act and as settlement increased, pressure grew on the U.S. government to remove the Indians from Florida. Seminoles offered sanctuary to blacks, and these became known as the Black Seminoles, and clashes between whites and Indians grew with the influx of new settlers. In 1832, the Treaty of Payne's Landing promised to the Seminoles lands west of the Mississippi River if they agreed to leave Florida. Many Seminole left at this time.
The Floridas
The Floridas was a region of the southeastern United States comprising the historical colonies of East Florida and West Florida. The borders of East and West Florida varied. In 1783, when Spain acquired West Florida and re-acquired East Florida from Great Britain through the Peace of Paris (1783), the eastern British boundary of West Florida was the Apalachicola River, but Spain in 1785 moved it eastward to the Suwannee River. The purpose was to transfer San Marcos and the district of Apalachee from East Florida to West Florida. From 1810 to 1813, the United States extended piecemeal control over the part of West Florida that comprised the modern-day Gulf coasts of Alabama and Mississippi and the Florida Parishes of Louisiana. After the ratification of the Adams-Onis Treaty in 1821 the United States combined East Florida and what had been the remaining Spanish-controlled rump of West Florida into the territory that comprised modern-day Florida.