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.
British America
British America gained large amounts of new territory following the Treaty of Paris (1763) which ended the French and Indian War in America, and ended British involvement in the Seven Years' War in Europe. At the start of the Revolutionary War in 1775, the British Empire included 20 colonies north and east of New Spain, including areas of Mexico and the Western United States. East and West Florida were ceded to the Kingdom of Spain in the Treaty of Paris (1783) which ended the American Revolution, and then ceded by Spain to the United States in 1819 after treaty negotiations to settle the old southwest border with Spanish Florida (eastern Louisiana, southern Alabama, Mississippi, and western Georgia). The remaining continental colonies of British North America to the northeast formed the Dominion of Canada by uniting provinces between 1867 and 1873. The Dominion of Newfoundland to the east joined Canada in 1949.