Why Was the Wilmot Proviso Important?

Important Wilmot Proviso

As the United States began the Mexican-American War in 1846, the long-suppressed issue over what to do with slavery re-emerged onto the national political scene. Just why was the Wilmot Proviso important regarding the issue of slavery and what controversy did it cause?

It was well-known in Congress that territorial acquisition from Mexico was a primary aim at the conclusion of the Mexican-American war. What was less certain was the how the expansion of slavery would be handled in any potential new territory gained.

The 1820 Missouri Compromise long-dominated the discussion on the limits of slavery. The compromise allowed Missouri to enter the Union as a slave state and Maine as a free state, but limited slavery to only the area below the parallel 36° 30’ north.

It was uncertain, however, if the Missouri Compromise line extended out further to the west into unorganized territories, or territory not yet controlled by the United States. 

In 1846, Pennsylvania representative David Wilmot proposed his now-infamous Wilmot Proviso, attempting to ban slavery in any territory acquired from the Mexican-American War.

Though the controversial Wilmot Proviso eventually failed, it is important in how it reignited the long-subdued issue of slavery in the United States, and forced it to become a major issue in American politics in the leadup to the Civil War.

Politics of the 1840s

Entering the 1840s, the Democratic party dominated the national political scene. Since the controversial election of 1800 where Thomas Jefferson won the presidency, the Democratic party controlled the White House.

All this changed when voters rejected Democratic incumbent Martin Van Buren in the election of 1840 following the disastrous effects of the Panic of 1837. The Whig Party under William Henry Harrison thus emerged triumphant.

When Harrison died just thirty-one days into office, Vice President John Tyler became President. As Tyler wandered from traditional Whig policies and was expelled from the party, both Whigs and Democrats prepared for a crucial election in 1844.

The primary concern for both parties in this election was the issue of slavery. Slavery was a long-dormant issue that always lingered behind the scenes on the national political scene.

David Wilmot Proviso
David Wilmot, Democrat from Pennsylvania via Wikimedia

The Democratic party at the time consisted of a coalition of several different groups that were formerly Jacksonian Democrats. This coalition bonded over their support of limited central government as well as support of increased individual liberties and state sovereignty.

Slavery would serve to be the major issue that drove a wedge into this coalition. Effectively three major groups in the Democratic party existed along sectional lines.

The Northeastern Democrats were led by former president Martin Van Buren and largely opposed slavery. John Calhoun led the Southern Democrats in the ardent pro-slavery stance. Finally, several figures led the Northwestern Democrats who were generally conciliatory towards slavery, so long as free states were added in conjunction.1

The primary reason that slavery was such a big issue in the election of 1844 was due to the impending question of the annexation of Texas. Texas was to be admitted as a slave state following their successful Texas Revolution, which greatly worried northerners of the further expansion of slavery.

The northeastern Democrats largely opposed the Texas annexation while the southerners favored it. Despite talk of fracturing for the election of 1844, the Democratic party was able to maintain the coalition by throwing support behind James K. Polk who vowed to annex Texas, as well as settle the Oregon boundary dispute with Great Britain to appease northerners.

With this support, Polk won the election and Congress quickly annexed Texas into the Union as a slave state. Relations once again quickly soured between northern and southern Democrats as Polk’s term progressed, leading to the infamous Wilmot Proviso.

What did the Wilmot Proviso Propose?

The Wilmot Proviso, introduced in 1846, proposed to ban slavery in any territory potentially acquired as a result of the Mexican-American War. The proviso is named after Pennsylvania Representative David Wilmot who introduced the bill for debate in Congress.

There is significant debate among historians as to who exactly originally proposed the proviso and whether Wilmot deserves all the credit.

Representative Jacob Brinkerhoff from Ohio claimed to be the true author of the proviso. Under Brinkerhoff’s assertion, he chose Wilmot to introduce the measure as the Speaker of the House would not allow Brinkerhoff to bring it to debate on the House floor given his well-known anti-slavery stance.2

The Wilmot Proviso attempted to ban slavery in lands acquired through the Mexican Cession. Map via Wikimedia

Wilmot was a well-known supporter of Polk’s administration, despite being a northern Democrat. His past support is what likely enabled him to bring the measure to the floor.

Most historians ultimately attribute the proviso to a group of northern Democrats. Preston King, Timothy Jenkins, and George Rathbun of New York, as well as Gideon Welles of Connecticut were also instrumental in the creation of the measure.2

We may never know the true author of Wilmot Proviso. Each of the representatives involved hand wrote out a copy of the measure and attempted to bring it to the House floor, hence the reason there are multiple “original” copies of the document.

Regardless of who helped, David Wilmot is the one that is immortalized through his introduction of the proviso.

Historians often question Wilmot’s motives. Why would an ardent supporter of Polk’s administration cause such controversy by introducing the Wilmot Proviso?

There likely was a significant personal ambition aspect to it. Wilmot was in hot water with his constituents over his support for Polk’s policies. The final Oregon resolution displeased the north and the Walker tariff of 1846 caused outrage in Pennsylvania.3

Wilmot’s reelection to Congress was in serious jeopardy given his support for Polk’s policies that his constituents opposed. Wilmot’s abrupt reversal of his slavery stance and introduction of the Wilmot Proviso may have been a way to save face and help his reelection campaign.

Why Was the Wilmot Proviso Important?

The Wilmot Proviso, which never passed, was important because it would have formally limited the expansion of slavery in the new territories expected to be gained from the Mexican-American war.

The measure was largely symbolic. Despite passing in the House of Representatives where anti-slavery supporters were the majority, the more evenly split Senate voted down the Wilmot Proviso.

Northerners reintroduced the measure twice more with the final attempt to attach it to the Treaty of Guadalupe-Hidalgo, but failed each time.

The Wilmot Proviso importance and votes chart

From a practical sense, there was no real reason to legislate slavery out of existence in the new territories in the American southwest. Given the geography and climate of the region, both northerners and southerners largely agreed that slavery could never flourish there.4

The Wilmot Proviso perhaps was a sign of northern Democrats’ displeasure with their declining influence on the national stage. It was also as close to a direct confrontation under the constitutional framework as could be possible at the time.

Northern Democrats led by Martin Van Buren grew frustrated with southern Democrats who increasingly demanded their northern allies support pro-slavery measures such as support for the Texas annexation. This put northern Democrats in a significant bind as they sought keep slavery as a non-issue among the rapid change in public opinion in the north.2

The Wilmot Proviso ultimately helped to further the sectional split between northern and southern Democrats, leading to the slow collapse of the party. The party finally fragmented and collapsed in the 1860 election.

Why Was the Wilmot Proviso so Controversial?

The Wilmot Proviso was so controversial as the attempt to prohibit slavery in the Mexican Cession territories incensed southern states. It helped to reignite the issue of slavery in national debate and caused southerners to cast a wary eye towards the north over the attempt to limit the expansion of slave states.

The introduction of the Wilmot Proviso by northern Democrats can be seen as revenge against southern Democrats for reneging on their commitments from the 1844 election.

When the Democrats united behind Polk in his 1844 election bid, it was with the understanding that northern Democrats would support the annexation of Texas, while southern Democrats would then support northern ambitions in settling the Oregon boundary dispute with Great Britain.1

After the north provided the votes to annex Texas, southern states reneged on their agreement and failed to support the north in their bid to have the Oregon boundary at the 54° 40’ north line.

The Oregon resolution, the passage of the Walker tariff, and Polk’s veto of the river and harbor bill all combined to convince the northern Democrats that Polk favored southern over northern interests.3

Zachary Taylor (left) wins the 1848 presidential election as Free Soil party leader Martin Van Buren hangs from the fence on his support over the Wilmot Proviso; via LOC

When Polk asked for $2 million in funds to facilitate negotiations with Mexico to end the Mexican-American war, northern Democrats saw this as a perfect opportunity to attach the controversial Wilmot Proviso to the appropriations bill.

While the Wilmot Proviso was certainly controversial at the time it was introduced, it was hardly the first time that limiting slavery in the western territories was proposed.

Even Thomas Jefferson proposed the expulsion of slavery in western territories in the land ordinance of 1784. While this measure was also rejected, limiting the expansion of slavery had been discussed since the very beginning of the United States.


To learn more about US history, check out this timeline of the history of the United States.


1) Persinger, Clark E. “The ‘Bargain of 1844’ as the Origin of the Wilmot Proviso.” The Quarterly of the Oregon Historical Society, vol. 15, no. 3, Oregon Historical Society, 1914, pp. 137–46, http://www.jstor.org/stable/20609962.

2) Eric Foner. “The Wilmot Proviso Revisited.” The Journal of American History, vol. 56, no. 2, [Oxford University Press, Organization of American Historians], 1969, pp. 262–79, https://doi.org/10.2307/1908123.

3) Stenberg, Richard R. “The Motivation of the Wilmot Proviso.” The Mississippi Valley Historical Review, vol. 18, no. 4, [Organization of American Historians, Oxford University Press], 1932, pp. 535–48, https://doi.org/10.2307/1898562.

4) Walker, Peter F. The North Carolina Historical Review, vol. 45, no. 1, North Carolina Office of Archives and History, 1968, pp. 99–101, http://www.jstor.org/stable/23518148.

Subscribe to our weekly newsletter!

Leave a Comment

Your email address will not be published. Required fields are marked *