Adams-Onís Treaty (1819): U.S. Acquires Florida, Sets Border with New Spain

The Adams-Onís Treaty (Transcontinental Treaty), signed February 22, 1819, resolved U.S.–Spanish territorial disputes. Negotiated by Secretary of State John Quincy Adams and Spanish minister Luis de Onís.

Key Provisions

1. Florida Cession: Spain ceded East and West Florida to the U.S. (U.S. assumed $5M in American citizen claims against Spain).
2. U.S.–New Spain Boundary: Defined from Gulf of Mexico up Sabine River to 32°N, then due north to Red River, west along Red River to 100th meridian, north to Arkansas River, west to its source, north to 42°N, then west to Pacific. This became the U.S.–Mexico border (1821) and later U.S.–Texas border.
3. Texas Relinquishment: U.S. renounced claims to Texas west of the Sabine—controversial at the time.
4. Oregon Country: U.S. gained Spanish rights north of 42°N (strengthening later claim vs. Britain).
5. Claims Settlement: Mutual release of pre-1819 claims; U.S. paid claims up to $5M.

Significance

• Completed U.S. Atlantic–Gulf coastal control
• Established first internationally recognized transcontinental U.S. boundary
• Delayed but did not prevent Texas independence (1836) and annexation (1845)
• Ratified 1821 (after Mexican independence); proclaimed 1822

The treaty reflected Adams' diplomatic mastery: maximizing territorial gain while avoiding war with Spain and (temporarily) appeasing Southern expansionists.