Adams‐Onís Treaty

Adams‐Onís Treaty (1819), also known as the Transcontinental Treaty, established the United States' first transcontinental boundary and acquired Florida.The treaty arose from a long‐standing territorial dispute between the United States and Spain over the precise boundaries of the Louisiana Purchase of 1803. Spanish officials, citing a prior agreement with France, first contested the legitimacy of Napoleon's sale of the Louisiana territory and then attempted to define its boundaries as the eastern bank of the Mississippi River (effectively nullifying the purchase) and excluding the province of West Florida, claimed by the United States. The Napoleonic Wars delayed negotiations until 1817, when they quickly became deadlocked.

Andrew Jackson's invasion of Florida during the First Seminole War of 1817–1818 broke the deadlock. Spain's minister to the United States and chief negotiator Don Luis de Onís, confronted by the prospect of losing Florida to American conquest, agreed to Secretary of State John Quincy Adams's proposed treaty, which ceded both East and West Florida to the United States and established a transcontinental boundary extending to the Oregon coast. In exchange, Adams gave up a dubious claim to Texas and assumed five million dollars in American citizens' claims against the Spanish government.

By resolving the dispute with Spain, the Adams‐Onís Treaty finalized the Louisiana Purchase. By conceding the claim to Texas, the agreement contributed to later agitation for the “reannexation of Texas,” which proslavery expansionists alleged had been wrongly given away. The western boundary established by the treaty acknowledged California and the Southwest as Mexican territory, setting the stage for the conquest of those lands by the United States in 1848.
See also Early Republic, Era of the; Expansionism; Foreign Relations: U.S. Relations with Europe; Texas Republic and Annexation.

Bibliography

Samuel Flagg Bemis , John Quincy Adams and the Foundations of American Foreign Policy, 1949.
William Earl Weeks , John Quincy Adams and American Global Empire, 1992.

William Earl Weeks