The Adams-Onis Treaty between the United States and Spain concluded all controversies regarding Spain's claims to Florida. Signed in Washington DC on February 22, 1819, by John Quincy Adams, the American secretary of state, and Luis de Onis, the Spanish minister, the treaty had three main effects.
- All Spanish claims to East Florida were abandoned and the territory ceded to the United States,
- The de facto control of West Florida, which had been in American hands since Andrew Jackson had established the American presence in 1818, was recognized, and
- a firm delineation of the border between the Louisiana Purchase and the remaining Spanish claims in North America was settled, beginning with the Sabine River between Texas and Louisiana.
The United States assumed the claims of its citizens against Spain, up to $5 million, and Pinckney's Treaty of 1795 was continued to the extent that it did not conflict.
The Spanish were not pleased with the treaty and delayed ratification while hoping to gain support from fellow European powers. None was forthcoming and after King Ferdinand was reduced to a constitutional monarch in 1820, Spain approved the treaty.