Adams-Onís Treaty Timeline

(1819–1821)

The Adams-Onís Treaty of 1819 settled territorial disputes between the United States and Spain, transferring Florida to the United States and establishing a boundary with Spanish Mexico. More Less

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Origins and negotiations

Pinckney's Treaty establishes Florida borders

1795

Pinckney's Treaty established borders between the United States and Spanish Florida, but continued American settlement in the region generated disputes that eventually contributed to negotiations over Florida and the broader southern boundary.

Image source: Pinckney's Treaty

Louisiana Purchase intensifies boundary disputes

1803

The Louisiana Purchase created disagreement over the new southern boundary of the United States. American and Spanish officials disputed whether the boundary ran along the Sabine River or as far south and west as the Rio Grande.

Image source: Louisiana Purchase

Peninsular War and independence wars weaken Spain

1807 - 1808

The outbreak of the Peninsular War in 1807, followed by the Spanish American wars of independence beginning in 1808, weakened Madrid's ability to defend and retain its American territories.

Image source: Peninsular War

United States annexes parts of West Florida

1810 - 1813

Between 1810 and 1813, the United States annexed West Florida in stages, extending from the Mississippi River eastward to the Perdido River, which later became the modern boundary with Alabama.

Image source: West Florida Controversy

First Seminole War leads to American occupation

1817 - 1818

During the First Seminole War, the United States occupied the rest of Florida. The occupation gave Secretary of State John Quincy Adams an opportunity to negotiate favorable terms with Spain.

Image source: Seminole Wars

Convention of 1818 opens settlement north of 42°

1818

The Anglo-American Convention of 1818 allowed both American and British citizens to settle land north of the 42nd parallel and west of the Continental Divide, helping establish the wider territorial context surrounding the Adams–Onís settlement.

Image source: Treaty of 1818

Spain accepts Florida's loss for a Texas boundary

1819

By 1819, Spain was prepared to accept the loss of Florida in exchange for a firm boundary in Texas, resolving major territorial disputes between the two countries.

Image source: Adams–Onís Treaty

Adams–Onís Treaty is signed

Feb 22, 1819

The Adams–Onís Treaty was signed by John Quincy Adams for the United States and Luis de Onís for Spain. The agreement settled territorial claims, transferred Florida to the United States, and defined a boundary extending westward toward the Pacific.

Treaty implementation

Madrid delays ratification

1819 - Oct 1820

Madrid delayed ratification until October 1820, hoping that diplomatic pressure would dissuade the United States from supporting anti-Spanish revolutionaries in the Americas.

U.S. Senate unanimously approves the treaty

Feb 24, 1819

The United States Senate approved the Adams–Onís Treaty unanimously two days after its signing, clearing the American constitutional requirement for ratification.

Claims commission distributes compensation

1821 - 1824

Under Article 11, the United States established a commission to process claims by private American citizens against Spain. Before dissolving in 1824, the commission distributed approximately $5 million.

Treaty becomes effective

Feb 22, 1821

After a proposal to defeat or alter the agreement was rejected, the Adams–Onís Treaty officially became effective on February 22, 1821.

Treaty provisions lose their original effect

Aug 24, 1821

The treaty's provisions remained in full effect only until August 24, 1821, when the Treaty of Córdoba acknowledged Mexican independence from Spain.

Monroe Doctrine articulates related principles

1823

The principles associated with American opposition to renewed European intervention in the Americas were set out in greater detail in the Monroe Doctrine of 1823.

Image source: Monroe Doctrine

Border consequences

Treaty of Córdoba recognizes Mexican independence

Aug 24, 1821

Spain recognized Mexican independence through the Treaty of Córdoba, signed on August 24, 1821. This ended the period in which Spain could fully control the territories involved in the Adams–Onís settlement.

Image source: Treaty of Córdoba

Russian claims south of 54°40′ are ceded

1824

The Russo-American Treaty of 1824 led the Russian Empire to cede its claims south of the 54°40′ north parallel to the United States, clarifying the northern Pacific context of the American territorial claim.

Image source: Russo-American Treaty of 1824

Treaty of Saint Petersburg sets Alaska's southern border

1825

The Treaty of Saint Petersburg established the southern boundary of Alaska on the same 54°40′ parallel. It also addressed Russian trading rights south of the line and British navigation rights north of it.

Image source: Treaty of Saint Petersburg (1825)

Mexico ratifies the treaty through the Treaty of Limits

1831

Although Mexico was not initially a party to the Adams–Onís Treaty, it ratified the settlement in 1831 by agreeing to the 1828 Treaty of Limits with the United States.

Image source: Treaty of Limits (Mexico–United States)

Texas independence leaves its eastern boundary unsettled

1836

The eastern boundary of Texas was not firmly established until the independence of the Republic of Texas in 1836, leaving an important part of the Adams–Onís boundary framework contested.

Image source: Republic of Texas

Guadalupe Hidalgo replaces parts of the boundary

1848

The Treaty of Guadalupe Hidalgo concluded the Mexican–American War and established the United States–Mexico boundary. It formalized Mexico's cession of Alta California and the present-day American Southwest, except for the later Gadsden Purchase territory of 1854.

Image source: Treaty of Guadalupe Hidalgo

Guadalupe Hidalgo replaces parts of the boundary

California adopts the 42nd parallel as its border

1850

Upon statehood in 1850, California established the 42nd parallel as its constitutional de jure northern border, preserving the line that had existed in 1819 when the region was part of Spanish Mexico.

Image source: California

Texas organizes Greer County

1860

In 1860, Texas organized the area later known as Greer County, reflecting continuing uncertainty over the boundary described by the Adams–Onís Treaty.

Image source: Greer County, Texas

Oregon–California border survey creates a dispute

1868 - 1870

A border survey conducted from 1868 to 1870 after Oregon's admission as a state made errors in demarcating and marking the Oregon–California boundary. The resulting dispute continues to the present day.

Later legacy

Supreme Court resolves Greer County claims

1896

The matter concerning Greer County was settled by a United States Supreme Court ruling in 1896, which upheld federal claims to the territory. The area was subsequently added to Oklahoma Territory.

Image source: Greer County, Oklahoma

Adams–Onís Treaty is formally terminated

1902

The Adams–Onís Treaty was formally terminated in 1902, although many of its boundary consequences had already been superseded or incorporated into later agreements.