Adams-Onis Treaty — Spain Cedes Florida to the United States and Drops Claims in the Oregon Territory

Adams-Onis Treaty Summary

The Adams-Onís Treaty was an agreement made in 1819 between the United States of America and Spain. The treaty is historically viewed as a significant diplomatic triumph for Secretary of State John Quincy Adams. The treaty addressed three major problems: the Floridas, Texas, and the western boundary of the Louisiana Purchase. Adams insisted that the Spanish cede both East and West Florida, arguing that West Florida was properly a part of the Louisiana Purchase and East Florida was being used to support American enemies. The boundary between Spain and the United States was settled at the Sabine River for Texas, as Adams did not receive support for a Spanish-American boundary that included Texas. Adams also pushed the boundary line out to the Pacific Ocean at the 42nd parallel, which strengthened the position of the United States in the Oregon Territory. When the treaty went into effect, the United States spanned the continent from the Atlantic Ocean to the Pacific Ocean and was a crucial step in fulfilling America’s Manifest Destiny.

Adams-Onis Treaty Facts

1. The Adams-Onis Treaty is also known as the Transcontinental Treaty.
2. The provisions of the treaty set new boundaries for the territory of the United States and New Spain.
3. Spain ceded East Florida and West Florida to the United States.
4. Spain dropped all claims to the Oregon Territory and the United States dropped claims to Texas.
5. United States territory spanned North America above the 42nd parallel.

Adams-Onis Treaty History and Overview

The Adams-Onís Treaty of 1819 was a significant milestone in the relationship between the United States and Spain. One result of the treaty was the acquisition of East Florida and West Florida by the United States.

Pinckney’s Treaty — the Treaty of San Lorenzo

Pinckney’s Treaty (1795) — also known as the Treaty of San Lorenzo, or the Treaty of Madrid — established the southern boundary between Spanish Florida and the United States at the 31st parallel. It was intended to be the border between the two countries from the Atlantic Ocean to the Mississippi River. The treaty also granted American merchants access to the port of New Orleans and the right to deposit goods in Spanish ports duty-free for up to three years.

Spain Weakened by the Napoleonic Wars

However, the line was not enough to ease tensions between the two nations. Although Spain controlled the Floridas, it did not prevent Americans from moving into the territory, especially West Florida. 

From 1807 to 1810, Spain was involved in the Peninsular War, which was part of the larger Napoleonic Wars in Europe. As a result, Spain reduced its military presence in the Floridas, significantly weakening its control.

West Florida Revolt of 1810

In 1810, the West Florida Revolt took place in West Florida. American settlers in the region rebelled against Spanish rule and declared independence from Spain. President Madison did not recognize the Republic of West Florida, but he did make a case that West Florida — from the Mississippi to the Perdido rivers — was part of the Louisiana Purchase. As a result, the United States occupied West Florida in December 1810 and annexed the territory.

United States Annexes the Mobile District

The Mobile District, along the coast of present-day Alabama and Mississippi, remained under Spanish control until 1813, during the War of 1812. Congress annexed the territory on February 12, 1813. The legislation authorized President Madison to send U.S. forces into the area. Madison sent General James Wilkinson to take control of Mobile in April. Wilkinson and around 600 men advanced on Mobile, which was surrendered by the Spanish. From that point on, Spain essentially abandoned the territory west of the Perdido River.

Negotiations Between the United States and Florida

In 1815, following the War of 1812, the United States and Spain opened negotiations. Don Luis de Onís (1762–1827), the Spanish Minister to America, represented Spain, while Secretary of State James Monroe represented the United States. However, negotiations were strained over Spain’s suspicions the United States was responsible for the West Florida Revolt.

Andrew Jackson Occupies West Florida

Monroe was elected President in 1816 and John Quincy Adams was named Secretary of State. In 1818, Andrew Jackson created an international incident when he seized Spanish forts at Pensacola and St. Marks during the First Seminole War. Jackson also had two British citizens executed on charges of helping to incite rebellion by the Seminoles and helping escaped slaves. 

President Monroe was critical of Jackson, but Secretary of State Adams defended Jackson. Adams believed Spain was at fault for failing to maintain order in its territory. Adams successfully used the American military in action to his advantage in the negotiations. He essentially demanded Spain exert control over East Florida or cede it to the United States. The negotiations focused on three major issues: 

1. Spanish cession of East Florida and West Florida — Adams insisted that Spain had to cede both East and West Florida to the United States. Onís raised several arguments against the cession of the Floridas, but he eventually agreed to the cession of East Florida and recognized American control of West Florida.
2. Spanish cession of Texas — Adams argued for a Spanish-American boundary that would have included Texas, but he settled for a boundary at the Sabine River, the western boundary of the present-day state of Louisiana. Adams reluctantly gave up Texas, not knowing that if he had pushed Onís hard enough, the Spanish minister would have conceded the territory.
3. The western boundary of the Louisiana Purchase — The third issue concerned the western boundary of the Louisiana Purchase, between the U.S. Territory and Spanish Territory. Adams and Onís based the boundary on a series of rivers and parallels, starting with the Sabine River. Adams pushed the boundary line out to the Pacific Ocean at the 42nd parallel, the southern boundary of the present-day state of Oregon.

In regards to Texas and Oregon, Spain gave up its claims in the Pacific Northwest in return for the United States giving up the attempt to acquire Texas. By extending the boundary to the Pacific Ocean, Adams strengthened the claim of the United States in the Oregon Territory, which was still claimed by Great Britain. It also moved U.S. Territory to within a few hundred miles of settlements in New Mexico, which helped open the Santa Fe Trail, and made American emigration to the Pacific Northwest and Oregon possible.

For the first time, the United States was able to claim that its territory stretched from the East Coast to the West Coast.

Adams-Onis Treaty Outcome

The treaty was signed on February 22, 1819, and approved by the U.S. Senate on February 24. As a result:

1. The U.S. took possession of both West Florida and East Florida, in return for agreeing to pay the legal claims of American citizens against Spain, up to $5 million. 
2. The U.S. abandoned its claims to Texas west of the Sabine River.
3. Spain gave up its claims to the Oregon Country.

After negotiations were concluded, the King of Spain, Ferdinand VII, granted most of the public lands in East Florida to three court favorites. Adams had overlooked a provision in the treaty that validated the grants and some controversy over the territory continued. 

The Spanish Revolution of 1820 led to a new Spanish Constitution. The new Spanish Government annulled King Ferdinand’s land grants and approved the Adams-Onis Treaty in 1821. Afterward, the U.S. Senate approved the treaty — now known as the Transcontinental Treaty — for a second time. President Monroe signed it and exchanged copies with Spanish officials in February 1821.

Adams-Onis Treaty Significance

The Adams-Onis Treaty is important to United States history because it added Florida to the United States and cleared Spanish claims to the Oregon Territory. When the treaty was finally ratified in 1821, it marked the first time the United States truly stretched from the East Coast to the West Coast.

Adams-Onis Treaty APUSH Study Guide

Use the following links and videos to study the Adams-Onis Treaty for the AP US History Exam.

Adams-Onis Treaty APUSH Definition

The Adams-Onis Treaty was an agreement signed on ‎February 22, 1819, between the United States and Spain that ceded Florida to the United States and established a new boundary between the United States and New Spain. 

Spain also agreed to drop its claims to the Oregon Territory and a new border was established between the United States and New Spain. When the treaty was ratified, the United States spanned the width of the continent, from the Atlantic Ocean to the Pacific Ocean.

American on the World Stage — The Adams-Onis Treaty

This video from Heimler’s History discusses the Adams-Onis Treaty for the AP US History Exam. Also, be sure to look at our Guide to the AP US History Exam.