Final answer:
The Wilmot Proviso, proposed by David Wilmot in 1846, was designed to ban slavery in territories acquired from Mexico, which intensified the national debate over slavery and highlighted the deepening North-South divide.
Step-by-step explanation:
The Wilmot Proviso was a significant legislative proposal made by Democrat Representative David Wilmot of Pennsylvania in 1846, aiming to prohibit slavery in any territory acquired from Mexico as a result of the Mexican-American War. It sparked considerable debate, passing in the House of Representatives but failing in the Senate. Party lines were often crossed as northerners generally supported the proviso, while southerners opposed it, indicating that regional loyalties overrode party affiliations when it came to slavery.
The introduction and repeated consideration of the Wilmot Proviso intensified national division, and it played a crucial role in pushing the country towards the sectional crises that would eventually culminate in the Civil War. It highlighted the growing split between the North and South and contributed to the rise of single-issue parties that focused on slavery and its expansion, such as the Free Soil Party. The discourse around the proviso also reflected differing views on slavery, with some northerners believing they honored the legacy of the founding fathers by restricting its growth and southerners defending slavery as a positive institution.