Final answer:
The Wilmot Proviso, an attempt to ban slavery in territories obtained from Mexico, was first introduced in Congress in 1846 by David Wilmot.
Step-by-step explanation:
The Wilmot Proviso was first brought up in Congress in 1846 by Democrat David Wilmot, a member of the U.S. House of Representatives. This significant legislative attempt aimed to prohibit slavery in any territory that would be acquired from Mexico following the Mexican-American War. Despite passing the House of Representatives, the Wilmot Proviso failed to pass in the Senate and resurfaced several times over the subsequent few years. It created a stark division between northern and southern politicians, regardless of party affiliation, and intensified the national debate on slavery.