Also called the Transcontinental Treaty of 1819, the Adams-Onis Treaty was the treaty that ended the Seminole Wars. It was negotiated by President James Monroe's United States Secretary of State John Quincy Adams and the Spanish foreign minister Luis de Onis. Spain was forced to negotiate because it was losing its grip on its colonial empire; its western colonies were primed to revolt. In its weakened state, it was fairly certain to lose the land to the United States in any case.
Under the terms of the treaty, Spain sold Florida to the United States for $5 million. The US agreed to assume financial claims by residents against the Spanish government. Spain also gave up its claims to Oregon north of the 42nd parallel (i.e., the northern border of California). For its part, Spain kept Texas, California and New Mexico, which at the time was an enormous region encompassing present-day Nevada, Utah, Arizona and parts of Colorado and Wyoming.
