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.
Spanish Florida
After American independence, the lack of specified boundaries led to a border dispute with the newly formed United States, known as the West Florida Controversy. The two 1783 treaties that ended the American Revolutionary War had differences in boundaries. The Treaty of Paris between Britain and the United States specified the boundary between West Florida and the newly independent U.S. at 31°. However, in the companion Peace of Paris between Britain and Spain, West Florida was ceded to Spain without its boundaries being specified. The Spanish government assumed that the boundary was the same as in the 1763 agreement by which they had first given their territory in Florida to Britain, claiming that the northern boundary of West Florida was at the 32° 22′ boundary established by Britain in 1764 after the Seven Years' War. The British line at 32° 22′ was close to Spain's old claim of 32° 30′, which can be justified by referring to the principle of actual possession adopted by Spain and England in the 1670 Treaty of Madrid. The now independent United States insisted that the boundary was at 31°, as specified in its Treaty of Paris with Britain.