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.
West Florida
On October 27, 1810, U.S. President James Madison proclaimed that the United States should take possession of West Florida between the Mississippi and Perdido Rivers, based on a tenuous claim that it was part of the Louisiana Purchase. (See "The U.S. claim", below.) The West Florida government opposed annexation, preferring to negotiate terms to join the Union. Governor Fulwar Skipwith proclaimed that he and his men would "surround the Flag-Staff and die in its defense". William C. C. Claiborne was sent to take possession of the territory, entering the capital of St. Francisville with his forces on December 6, 1810, and Baton Rouge on December 10, 1810. Claiborne refused to recognize the legitimacy of the West Florida government, however, and Skipwith and the legislature eventually agreed to accept Madison's proclamation. Congress passed a joint resolution, approved January 15, 1811, to provide for the temporary occupation of the disputed territory and declaring that the territory should remain subject to future negotiation.