As the United States grew and expanded into new territories in the early to mid-19e century, the divisions also deepened. At the heart of these divisions is the issue of slavery. In 1846, a representative from Pennsylvania named David Wilmot proposed legislation to ban the expansion of slavery in lands acquired after the Mexican-American War.
The Wilmot Reservation was not adopted, and debate over the proposal heightened North-South tensions. “It’s part of a larger, broader discussion about the future of slavery,” says Dr. Miller W. Boyd III, a historian, teacher, and lecturer in St. Louis, Missouri. “It’s a small link in a long chain that goes towards civil war.”
Competing economic priorities in the North and the South
Slavery became a hotly contested issue between North and South, largely because different economic realities prevailed in different regions. The northern economy was more focused on industry and manufacturing, while crops like tobacco and cotton were big moneymakers for white Southerners.
“In Pennsylvania, for example, people grew wheat. Wheat is not a labor intensive crop. Slaves were almost incidental to society,” Boyd explains. “In a place like Louisiana or Virginia, you don’t have a society with slaves, you have a society of slaves. Everything is determined or shaped around movable slavery.
These differences in economic priorities influenced how slavery was viewed and the degree to which it was tolerated or considered necessary in various parts of the country.
Wilmot Clause: Limiting the Spread of Slavery

A certificate of membership in the Wide-Awake Club, a Republican marching club formed in 1860 and dedicated to the preservation of the Union and the non-extension of slavery for members of the Free Soil Party.
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The first abolitionists were usually northerners who opposed slavery on religious and moral grounds. They recognized the humanity of enslaved people, the inhumanity of slavery, and saw the contradiction of allowing such a racist system to persist in a country founded on the principle that “all men are created equal “.
Southerners enjoyed exponentially the economic benefits of maintaining a compulsory bonded labor force and most were unwilling to see slavery abolished. They resented attempts to reduce it – arguing that slavery was the blood of their economy and an integral part of their way of life. This position paved the way for the Confederacy and its eventual secession from the United States.
Wilmot was not an abolitionist or an advocate of slavery. He and his affiliates, as members of the Free Soil Party, were not fighting to preserve or abolish slavery. They were content to let slavery persist, but they wanted to keep it from spreading as America expanded into new territories. Wilmot and those aligned with him wanted to create and preserve economic opportunity for white citizens.
“Wilmot wanted more land available for poor and average white people to farm,” Boyd explains. “He was trying to help them not have to compete everywhere with crops produced by slaves.” Because wherever slavery might have flourished, it took jobs and suppressed working class wages. Wilmot and his affiliates were also concerned that the slave states had gained too much political power and wanted to see that influence reduced.
New Land after the Mexican-American War

A color-coded map from 1909 shows the gradual acquisition of territory by the United States, including the Mexican cession of 1848.
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So when, in August 1846, President James Polk introduced a special appropriations bill asking Congress for $2,000,000 to acquire territory from Mexico as part of peace negotiations after the Mexican-American War, the Wilmot’s conditional clause sought to prevent slavery from spreading to any of this newly acquired land.
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“This war was fought for the acquisition of territory and the hope of expanding not only American borders, but also slavery,” says Boyd.
Wilmot was a member of a Democratic party that had split into opposing factions over the issue of slavery in the 1844 election. This divide was further entrenched when President Polk accepted less land in a compromise with the Great Britain involving Oregon, while seeking a larger percentage of Texas in Mexico.
Northern Democrats like Wilmot worried about the implications of the United States acquiring additional territories where slavery would be permitted. In sponsoring the Wilmot Proviso, Wilmot was acting on behalf of his constituents, namely, white and free Pennsylvanians.
(See the full text of Wilmot’s reservation as preserved by the National Archives.)
Wilmot Proviso fails, tensions erupt
The Wilmot Proviso was dead in three days. It passed twice in the US House of Representatives, where Northerners had a majority. But that failed in the US Senate where there was equal support for free states and slave states. Polk’s “Propriation to Secure Peace Bill” was passed in early 1847 without Wilmot’s proviso.
Although the 1846 Wilmot Reserve was not passed with Polk’s appropriations bill, it still left a lasting legacy. The objective of the proposed amendment was simple and straightforward: slavery and involuntary servitude would be banned forever in all territories acquired as a result of the Mexican-American War. The only exception (much like in the 13th Amendment) would be unpaid labor as punishment for a crime.
The similarity in the wording of these two documents is not fortuitous. The 13th Amendment borrowed some of its language from Wilmot’s reservation, which in turn took some of its language from the North-West Ordinance of 1787.
Although Wilmot’s proviso failed on its own, it fueled a volatile division and debate between Northern and Southern states over slavery and ultimately made Civil War more inevitable. It also spurred the creation of the Republican Party because, as Boyd explains, “the Republican Party was the culmination of this anti-slavery, abolitionist, but also mostly Free Soil rhetoric.”
The Wilmot reservation exposed competing economic interests that inflamed North-South tensions around the issue of slavery, brought the country closer to civil war, and continued to divide America long after the 13th Amendment was ratified.
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Wilmot Condition, UShistory.org.
The Wilmot Reserve, NBC News Learn.
Wilmot Provision Transcript, National Archives of the United States.
“How are US states, territories, and commonwealths referred to in the Geographic Names Information System?” » USGS.