When America Finally Turned Against Slavery – The Wilmot Proviso by Gregory Hilton

The February 1848 Treaty of Guadalupe Hidalgo ended the Mexican War. The United States acquired tremendous new territory and at the end of the year war hero Zachary Taylor would be elected as America's last Whig President.

“Nothing is more powerful than an idea whose time has come.” – Victor Hugo.

Passage of the Wilmot Proviso in the House of Representatives was truly a great moment in America history. It is one of the few Congressional debates which completely changed the political landscape. All of the old issues (the tariff, a national bank and internal improvements) were placed on the back burner. House voting patterns and party loyalties radically changed, and slavery now dominated the Congressional agenda.
Lawmakers would no longer be voting as Democrats or Whigs and a major upheavel had begun. Afterwards it would be northerners against southerners, and there would be no turning back to the days when slavery was tolerated. It would take another two decades for the battle against slavery to succeed, but with the Wilmot Proviso the debate had finally begun.
What Was The Wilmot Proviso?
Rep. David Wilmot (D-PA) earned his unique place in the annals of the U.S. Congress on Saturday evening, August 8, 1846. The Proviso offered by the freshman lawmaker said “neither slavery nor involuntary servitude shall ever exist in any part of said territory.” The House was debating a last minute request from President James K. Polk (D-TN) for $2 million to compensate Mexico for new territory.
The Mexican War had begun four months earlier, and a victory would not be secured for another two years. The final appropriation would be $15 million and the new territory would include present-day California, Nevada and Utah and parts of New Mexico, Arizona, Texas, Colorado and Wyoming.
The anti-slavery movement was always a significant factor in American politics but its prospects for success appeared dim until 1846 when the Wilmot Proviso passed the House of Representatives. At the 1787 Constitutional Convention it was agreed that slaves would be counted as only 3/5’s of a man for census purposes.
The Founding Fathers also agreed to abolish the importation of slaves after 20 years, and this went into effect in 1808. However, this had no impact on the internal trade and by 1846 there were almost 4 million slaves in the United States.
Many Americans had been speaking out against slavery in the 70 years before Wilmot introduced his Proviso. One of the lawmakers who listened to Wilmot’s plea that evening was former President John Quincy Adams. He had only 18 months to live, and had headed up the House abolitionist forces for the past 16 years.
Wilmot did not say anything new. All of his arguments had previously been made by Adams and other abolitionists. What was new was the future territory to be gained by the Mexican Cession, and that lawmakers were finally ready to vote against the expansion of slavery.
Why Was The Wilmot Proviso Important?
While many other lawmakers had denounced slavery, the Wilmot Proviso was the first blow against the “peculiar institution” to be passed by the House of Representatives. The Polk Administration immediately knew they were in trouble after the Proviso was introduced, and three cabinet members rushed to the House floor to lobby against Wilmot’s proposal.
The Proviso passed the House by an 85 to 80 margin, and every negative vote except three came from slave states. While the Wilmot Proviso passed the House in both the 29th and 30th Congresses, it was never enacted by the Senate.
The Proviso had a huge impact because all of the dominant political issues of the day were placed on the back burner. The expansion of slavery was now America’s number one concern. Both major parties would be split along sectional lines.
In The Slavery Issue, Michael Holt would say the Proviso “utterly shattered” both Democrats and Whigs. The opposition bible, the Boston Whig, correctly noted “As if by magic, the Proviso brought to a head the great question which is about to divide the American people.”
Many of the lawmakers who supported Wilmot in 1846 would achieve prominence 15 years later during the Abraham Lincoln administration. More senior lawmakers were the real authors of the Proviso but their opposition to slavery was well known. They selected Wilmot as the author because he was certain to gain recognition to speak during the two hours which had been alloted for debate.
The debate begun by Wilmot would not end until the Civil War. A huge split occurred in the Democratic Party when its 1848 convention failed to adopt the Wilmot Proviso. Northern Democrats were in revolt and they walked out of the convention and formed the Free Soil Party with former President Martin Van Buren as their candidate. Its platform was “No more slave states and no more slave territory.”
The split allowed the election of America’s last Whig president. While the Whigs won the next election they were also doomed because of a regional divide.
The Wilmot Proviso eventually was expanded to include all of the western territories and it resulted in the Compromise of 1850. California was admitted as a free state, the other territories were allowed to decide for themselves if they wanted to be slave or free states, and a Fugitive Slave Act was adopted requiring all citizens to assist with the capture of runaway slaves. The Compromise of 1850 was repealed by the passage of the 1854 Kansas-Nebraska Act which once again brought Wilmot’s proposal to the forefront.
This legislation would have allowed slavery in the new territories by “popular sovereignty.” The northern states were outraged by the Kansas-Nebraska Act and one of its effects was the incorporation of the Free Soil Party into a new anti-slavery Republican Party. The Wilmot Proviso was ruled unconstitutional in the highly controversial 1857 Dred Scott decision of the U.S. Supreme Court.
The court said Congress was not allowed to ban slavery in the new territories because slaves were personal property and they could never be citizens of the United States. The Wilmot Proviso was eventually enacted in 1862, 16 years after it first passed the House.
The House of Representatives has seen many outstanding freshman lawmakers. Henry Clay (KY) was elected Speaker as a freshman. Rep. J. William Fulbright (D-AR) was a freshman when Congress adopted the admirable scholarship program which still bears his name. Nevertheless, it would be hard to name another freshman who has had a greater impact on American history than David Wilmot.
What Happened to David Wilmot?
Prior to the Proviso he had been a loyal supporter of the Polk Administration. He was the only Democratic Congressman from Pennsylvania to back the President’s tariff reductions. Wilmot was against the expansion of slavery but in 1846 he was not advocating an end of slavery.
Wilmot served in the House for three terms (1844 to 1850), and was later a member of the Free Soil Party before becoming one of the founders of the Republican Party. He was the first Republican candidate for Governor of Pennsylvania, and had a key role in the 1860 presidential nomination of Abraham Lincoln. Wilmot turned down an opportunity to serve in Lincoln’s cabinet and was instead elected to the U.S. Senate. He filled the vacancy caused by the resignation of Sen. Simon Cameron (R-PA) who was Lincoln’s first Secretary of War.

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