Why were members of Congress concerned with slavery expanding in the west territories won from Mexico?

The expansion of slavery into the lands we received as a result of the war with Mexico was a big concern for the members of Congress. In 1846, David Wilmot proposed that slavery would be banned in any territory we would receive from Mexico as a result of our war with Mexico. The North supported this idea, and the South was against it. While it did pass in the northern-dominated House of Representatives, the Wilmot...

The expansion of slavery into the lands we received as a result of the war with Mexico was a big concern for the members of Congress. In 1846, David Wilmot proposed that slavery would be banned in any territory we would receive from Mexico as a result of our war with Mexico. The North supported this idea, and the South was against it. While it did pass in the northern-dominated House of Representatives, the Wilmot Proviso didn’t pass in the Senate because it couldn’t get a majority of votes in the Senate that was equally divided between free states and slave states. This shows how big of a concern this issue was for the members of Congress.

The northerners were very concerned that several states might be created from the territory we gained as a result of the war with Mexico. This would give the South an opportunity to possibly pass laws that were favorable to slavery and slave owners. Since much of this land we might gain from Mexico would be favorable for farming and the growing of cotton, the northerners in Congress were really concerned that slavery could expand to several states that might be created from the territory we got from Mexico. If that happened, northerners could be put at a big disadvantage. The issue of the expansion of slavery was a big concern for members of Congress.