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Definition of Adams-Onis Treaty



The Adams-Onis Treaty was an agreement between the United States and Spain signed in 1819 which established the southern border of the Louisiana Purchase. As part of the agreement, the United States obtained the territory of Florida.

The treaty was negotiated in Washington, D.C. by the American secretary of state, John Quincy Adams, and the Spanish ambassador to the United States, Luis de Onis.

Background of the Adams-Onis Treaty

Following the acquisition of the Louisiana Purchase during the administration of Thomas Jefferson, the United States faced a problem, as it was not entirely clear where the border lay between the territory obtained from France and the territory of Spain to the south.

Over the first decades of the 19th century, Americans venturing southward, including Army officers (and possible spy) Zebulon Pike, were apprehended by Spanish authorities and sent back to the United States. A clear border needed to be defined.

And in the years following the Louisiana Purchase, the successors to Thomas Jefferson, James Madison and James Monroe, sought to acquire the two Spanish provinces of East Florida and West Florida.

Spain was barely holding on to the Floridas, and thus was open to negotiating a treaty which would trade away that land in return for clarifying who owned land to the west, in what today is Texas and the southwestern United States.

Negotiation of the Treaty

The Spanish ambassador in Washington, Luis de Onis, had been granted full power by his government to make a deal, and he met with John Quincy Adams, secretary of state to President Monroe. The negotiations were disrupted and nearly ended when a military expedition led by Andrew Jackson ventured into Florida.

When negotiations resumed they were fruitful, and Adams and Onis signed their agreement on February 22, 1819. A compromise boundary was established between the U.S. and Spanish territory, and the United States gave up claims to Texas in exchange for Spain giving up any claim to territory in the Pacific Northwest.

The treaty, after ratification by both governments, became effective on February 22, 1821.

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