Following the Lewis and Clark Expedition (1804-1806), the boundaries of the Louisiana Purchase remained contested. Expansionists chose to believe the purchase included vast stretches of land, including all of Spanish Texas. The Spanish government disagreed, however. The first attempt to resolve this issue took place in February 1819, with the signing of the Adams-Onís Treaty, which was actually focused on settling the problem of Florida.

Spanish Florida

Spanish Florida had presented difficulties for its neighbors since the settlement of the original North American colonies, first for England and then for the United States. By 1819, American settlers no longer feared attack by Spanish troops garrisoned in Florida, but hostile tribes like the Creek and Seminole raided Georgia and then retreated to the relative safety of the Florida wilderness. These tribes also sheltered runaway enslaved persons, often intermarrying with them and making them members of their tribes. Sparsely populated by Spanish colonists and far from both Mexico City and Madrid, the frontier in Florida proved next to impossible for the Spanish government to control.

In March 1818, General Andrew Jackson, frustrated by his inability to punish Creek and Seminole raiders, pursued them across the international border into Spanish Florida. Under Jackson’s command, U.S. troops defeated the Creek and Seminole, occupied several Florida settlements, and executed two British citizens accused of acting against the United States. Outraged by the U.S. invasion of its territory, the Spanish government demanded that Jackson and his troops withdraw. In agreeing to the withdrawal, however, U.S. Secretary of State John Quincy Adams also offered to purchase the colony. Realizing that conflict between the United States and the Creeks and Seminoles would continue, Spain opted to cede the Spanish colony to its northern neighbor. The Adams-Onís Treaty, named for Adams and the Spanish ambassador, Luís de Onís, made the cession of Florida official while also setting the boundary between the United States and Mexico at the Sabine River. In exchange, Adams gave up U.S. claims to lands west of the Sabine and forgave Spain’s $5 million debt to the United States.

Figure 1. The red line indicates the border between U.S. and Spanish territory established by the Adams-Onís Treaty of 1819.

American action in Florida seized Indigenous people’s eastern lands, reduced lands available for freedom-seeking enslaved people, and killed entirely or removed Native American peoples farther west. This became the template for future action. Presidents, since at least Thomas Jefferson, had long discussed removal, but President Andrew Jackson took the most dramatic action. Jackson believed, “It [speedy removal] will place a dense and civilized population in large tracts of country now occupied by a few savage hunters.”^[1] Desires to remove Native Americans from valuable farmland motivated state and federal governments to cease trying to assimilate Native Americans and instead plan for forced removal.

The Adams-Onís Treaty upset many U.S. expansionists, who criticized Adams for not laying claim to all of Texas, which they believed had been included in the Louisiana Purchase. In the summer of 1819, James Long, a planter from Natchez, Mississippi, became a filibuster, or a private, unauthorized military adventurer, when he led three hundred men on an expedition across the Sabine River to take control of Texas. Long’s men succeeded in capturing Nacogdoches, writing a Declaration of Independence (see below), and setting up a republican government. Spanish troops drove them out a month later. Returning in 1820 with a much smaller force, Long was arrested by the Spanish authorities, imprisoned, and killed. Long was but one of many nineteenth-century American filibusters who aimed at seizing territory in the Caribbean and Central America.