Mexican American War
The Mexican–American War, which was otherwise known as, "Mr. Polk's War", was initially opposed by Northern Whigs. They felt that it was a war to extend slavery. David Wilmot introduced a proviso in the appropriations bill that stated: "as an express and fundamental condition of the acquisition of any territory from the Republic of Mexico... neither slavery nor involuntary servitude shall ever exist in any part of said territory." Congressman Gideon Welles of Connecticut spoke out in support of the proviso stating: "The time has come, when the Northern democracy should make a stand. Every thing has taken a Southern shape and been controlled by Southern caprice for years. We must satisfy the Northern people that we are not to extend the institution of slavery as a result of this war."
The vote on the Wilmont proviso came out on straight sectional lines. The bill passed the House of Representatives. However, the Congress adjourned before the Senate could take up consideration of the bill. In 1847 the proviso was reintroduced. Again, the bill was passed by the House. However, the Senate that was dominated by Southerners, voted against the proviso. A number of House Democrats were pressured to reverse themselves – (to allow the appropriation vote to go forward without the proviso.) The crisis had been averted for the moment. However, the fury that the Mexican war had unleashed was clear even to President Polk. Polk wrote in his diary: "The slavery question is assuming a fearful aspect. It cannot fail to destroy the Democratic party, if it does not ultimately threaten the Union itself. "