Final answer:
In 1846, Congressman David Wilmot proposed the Wilmot Proviso to prohibit slavery in all territories acquired from Mexico, which passed the House but failed in the Senate and intensified national debate over slavery.
Step-by-step explanation:
In 1846, Congressman David Wilmot proposed the Wilmot Proviso, which sought to prohibit slavery from all territories acquired from Mexico. This legislative proposal was introduced as an amendment to an appropriations bill and passed in the House of Representatives but failed in the Senate. Although it never became law, the debate surrounding the Wilmot Proviso intensified the sectional tensions between the North and South and contributed to the discussion on the future of slavery in the United States. The proviso had northern support as it aligned with interests to keep western territories free of slavery for the benefit of White laborers.
The significance of the Wilmot Proviso lay in its clear stance against the expansion of slavery, reinvigorating the slavery issue in national politics and ultimately contributing to the ascension of new single-issue parties like the Free-Soil Party. Despite its failure to become law, the Wilmot Proviso became emblematic of the deep divisions regarding slavery, which persisted up to the Civil War. Notably, Congressman Wilmot's efforts reflected a broader antislavery sentiment, where the principle of restricting the spread of slavery in new territories was paramount.