Politics During the Mexican-American War

The event that set the stage for the proposal of the Wilmot proviso was James K. Polk's request for $2 million for his negotiations. Meanwhile, both Democrats and Whigs were very careful to avoid issues like slavery for fear of causing a split within the party. The Wilmot Proviso forced a debate over these very issues, making the parties fears realized.

The State of Politics and Parties

The annexation of Texas at the tail end of John Tyler's presidency plunged America into war with Mexico. Polk, the next president from the Democratic Party, gained a Democrat-controlled government as well. That would not mean, however, that conflict will be totally absent.

A Democratic-Controlled Government

Although both the House and Senate had a Democratic majority, there were other factors present that prevented a wholly united Congress. In particular, the sectional (North/South) divides within the parties. As a result, representatives, congressmen, and party leaders worked hard to ensure divisive issues such as slavery would be avoided.
Because of these sectional divides, we can split the Democratic Party into two subgroups: The Northern Democrats and the Southern Democrats. James K Polk, a Southern Democrat, drew contempt from the Northern Democrats as he seemed to be serving largely Southern interests.

Northern Democrats vs. Southern Democrats

The Northern Democrats themselves could be split into two groups as well: the anti-slavery Barn-burners and the more conservative Hunkers. When it came to sectional issues, Northern Democrats were expected to follow the South's lead, and people who did were commonly referred to as doughfaces. These doughfaces were necessary for Southern Democrats to have a lead in the Senate and keep the more Northern House in check.

A Weak Whig Party

Meanwhile the Whigs were still recovering from Henry Clay's defeat in the election. The Whig's failure to take a strong stance regarding Texas's annexation was a key element of its defeat, but they were afraid debate on Texas would bring up the issue of slavery. The Whig's goal was to conceal its North/South divisions within the party by actively avoiding the topic of slavery all together.