Introduced by Congressman David Wilmot, but never enacted, the Wilmot Proviso would have banned the spread of slavery into territories Mexico ceded to the U. S. after the Mexican-American War.
The U.S. Constitution and Slavery
When delegates to the Constitutional Convention assembled in Philadelphia in 1787, one of the more daunting tasks that they faced was resolving sectional differences between the North and South centered on the issue of slavery. After weeks of debate proved futile, the delegates negotiated a series of compromises that enabled them to proceed with their primary assignment of forming "a more perfect Union" between the separate states. In the short term, the compromises regarding the status of slavery established in the Constitution facilitated the creation of the new republic (at the expense of blacks held in bondage), but they also sowed the seeds of turmoil that began coming to fruition as the nation expanded west in the coming decades.
The Northwest Ordinance
As the delegates to the Constitutional Convention set about creating a new government, representatives to the Congress of the existing government established under the Articles of Confederation were meeting in New York. On July 13, 1787, the Confederation Congress enacted "An Ordinance for the government of the Territory of the United States northwest of the River Ohio," that stipulated "There shall be neither slavery nor involuntary servitude in the said territory. . . ." That legislation, more commonly known as the Northwest Ordinance, had the effect of establishing the Ohio River as the border separating free and slaves states between the Appalachian Mountains and the Mississippi River. For the next three decades, that boundary forestalled major sectional disputes over slavery.
The Louisiana Purchase
Circumstances changed in 1803 when Napoleon Bonaparte sold President Thomas Jefferson 828,000 square miles of land west of the Mississippi River. In hindsight, the Louisiana Purchase may be seen as a logical progression of the American Westward Movement, but at the time, it created new challenges for the Federal government. In addition to land ownership issues regarding the native inhabitants, Congress eventually was forced to address the subject of slavery in the new territory.
The Missouri Compromise
In 1818, the residents of Missouri petitioned Congress for statehood. An estimated 8,000 to 10,000 slaves lived in the territory at that time. Southerners expected Missouri to be admitted as a slave state, but New York Congressman James Tallmadge introduced an amendment to the Missouri statehood measure that would have gradually ended slavery in the new state. The Tallmadge Amendment initiated a year of acrimonious debate in both houses of Congress. Legislators finally reached a compromise in 1820, admitting Maine as a free state and Missouri as a slave state. Wishing to avoid similar conflicts in the future, Congress also prohibited slavery in the remainder of former Louisiana Territory, north of the southern border of Missouri (36°30' north latitude). Although not a perfect solution in the minds of all parties (especially abolitionists), the Missouri Compromise muffled the debate over the extension slavery in the United States for more than three decades.
The Mexican-American War
Things changed in 1846 when the U.S. initiated a war with Mexico that was destined to greatly expand American territorial possessions in the West. Mexico and the U.S. had been at odds over Texas since 1836, when Texans won a war for independence from the Mexican government and established the Lone Star Republic. Although the U.S., along with England and France, recognized the new republic, Mexico had designs on re-conquering the territory that was lost. In 1845, despite warnings from Mexico, Texans encouraged the U.S. Congress to annex the republic. When a dispute emerged over the border between Texas and Mexico, President James K. Polk sent 3,500 U.S. troops into Texas to prevent a Mexican invasion. In November, Polk attempted to avoid hostilities by offering to purchase land that would settle the Texas border dispute, along with Mexican territories in the West coveted by the United States. Mexican officials dismissed Polk's overtures. With war appearing to be imminent, Texans accepted an offer of annexation by the U. S. and became the 28th state on December 29, 1845.
The Wilmot Proviso
The border dispute remained at an impasse over the winter, but on April 25, 1846, a Mexican cavalry force attacked a U.S. patrol that Polk had deployed into the contested territory between the Rio Grande and the Nueces River. Polk requested a declaration of war, and Congress obliged on May 13, 1846. A little less than; three months later, on August 6, Polk submitted a request to Congress to appropriate $2,000,000 to negotiate the end of the war by purchasing from Mexico the land he coveted. On August 8, Pennsylvania Congressman David Wilmot introduced an amendment to Polk’s request. Modeled after language from the Northwest Ordinance passed by the Continental Congress in 1787, the Wilmot Proviso stipulated the following:
Provided, That, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the moneys herein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime, whereof the party shall first be duly convicted.
House members voted to add the proviso to Polk's bill by a margin of 83–64, and then approved the entire bill by a vote of 85–80.
On its face, support of Wilmot's Proviso appeared to be a repudiation of the extension of slavery, but there were other political motivations behind the vote. A significant number of northern politicians had axes to grind with Polk. Northern members of his own party believed that Polk's supporters had unfairly wrested the 1844 Democratic presidential nomination from New York's Martin Van Buren. Polk further alienated Northern Democrats when he handed out patronage positions in New York to his Southern followers instead of to local Van Buren backers. Beyond internal party issues, many Northerners, Whigs and Democrats alike, believed that Polk's administration was too pro-South. His cabinet was dominated by Southerners. Polk supported lower tariffs and opposed internal improvements at the expense of the North. Furthermore, Polk had settled for a compromise agreement in a dispute with Great Britain over the northern border of Oregon, at the same time that he was promoting war with Mexico to expand Southern territories. Whig leaders fixed on this apparent inconsistency as an opportunity to level charges that the war with Mexico was being fought to extend slavery in the United States. Northern Democrats, well aware that those charges could prove damaging in the upcoming Congressional election of 1846, added their weight to the amendment.
After adoption by the House of Representatives, Polk's appropriation request, including the Wilmot Proviso, was sent on to the Senate, which was evenly split along sectional lines. Southerners successfully extended debate on the matter until the House adjourned for the season, thus ending the current session of Congress and, thereby, killing the bill.
When Congress reconvened in1847, Polk submitted a $3,000,000 request for funds to end the war with Mexico. Northern Democrats led by Hannibal Hamlin and Preston King reintroduced a revised version of Wilmot's Proviso that excluded slavery in "any territory on the continent of America which shall hereafter be acquired." The House then passed Polk's "Three Million Dollar Bill" along with the attached proviso by a vote of 115–106. In the Senate, where Southerners and Northerners held an equal number of votes, the anti-slavery measure was stripped from the legislation. Southerners then succeeded in twisting enough arms in the House to get the Senate version passed.
Controversy over the Wilmot Proviso erupted again in 1848 when the Mexican-American War ended and the administration sent the Treaty of Guadalupe-Hidalgo to the Senate for ratification. Northerners attempted to interject the language of the proviso into the treaty, but Southerners again prevailed. The acquisition of new territories from Mexico after the war amplified the debate over the extension of slavery, and the Wilmot Proviso evolved as a rallying cry for anti-slavery activists. Bloodshed was averted by the enactment of the Compromise of 1850, but as Senator Salmon P. Chase guardedly observed, "the question of slavery in the territories has been avoided. It has not been settled."
Because of its central role in the debate over slavery, the Wilmot Proviso may well be the most significant piece of legislation never passed by the U.S. Congress. Ominously, the measure was consistently defeated along sectional, rather than party lines. By crystallizing the sectional differences that existed over slavery, the proviso transformed the political landscape in the U.S., beginning with the demise of the Whig Party and the emergence of the Free Soil Party, which eventually evolved into the Republican Party. Free-Soilers and Republicans adopted platforms advocating the congressional prohibition of slavery from all federal territories, giving the opponents of slavery a clear political option. Often characterized as "Black Republicans" by Southerners, supporters of the proviso also provided proponents of slavery with a distinctively identifiable opposition. While the Whigs were busy disintegrating, the Democratic Party did not escape unscathed. During the 1850s, Democrats gradually came to define themselves based upon their stance on the extension of slavery. Sectional differences hastened the division of the Democratic Party during the Election of 1860, enabling Abraham Lincoln to ascend to the presidency with less than forty percent of the popular vote, kindling the American Civil War.