The Adams Onis Treaty was concluded 190 years ago today (1819). It ceded Florida to the United States and settled, after nearly 16 years, the boundaries of the Louisiana Purchase.
His Catholic Majesty [Spain] cedes to the United States, in full property and sovereignty, all the territories which belong to him, situated to the eastward of the Mississippi, known by the name of East and West Florida.
The boundary-line between the two countries, west of the Mississippi, shall begin on the Gulph of Mexico, at the mouth of the river Sabine, in the sea, continuing north, along the western bank of that river, to the 32d degree of latitude; thence, by a line due north, to the degree of latitude where it strikes the Rio Roxo of Nachitoches, or Red River; then following the course of the Rio Roxo westward, to the degree of longitude 100 west from London and 23 from Washington; then, crossing the said Red River, and running thence, by a line due north, to the river Arkansas; thence, following the course of the southern bank of the Arkansas, to its source, in latitude 42 north; and thence, by that parallel of latitude, to the South Sea [Pacific].
The Avalon Project has the complete text of the Treaty. The Adams in the Treaty short name is Secretary of State John Quincy Adams.
Thanks for posting about this. I have been studying the Adams-Onís Treaty this week, and all the border disputes that led up to it. There’s a fascinating map at the Library of Congress from Dr. John Robinson, an army surgeon who also apparently became enchanted with Mexico after being captured in New Mexico with Zebulon Pike’s expedition. He tried to defect, then served as a secret agent/ special envoy to Mexico for James Monroe, and later a brigadier-general in the Mexican Republican Army. He was very vocal in support of Mexican independence from Spain & published the first map showing the southern boundaries of the US, as a political statement against the cessions to Spain, which amounted to over 1 million acres. The US border could have ended up along the Rio Grande, which would have put most of New Mexico (Taos, Santa Fe, Pecos, Galisteo, Albuquerque, etc.) in the US, with Atrisco, Belen, and Socorro in Spain.
Map is here; the blue lines show the contested area, and the red line is the Adams-Onís treaty.