7. The Wilmot Proviso (1846)
In August 1846, Representative David Wilmot of Pennsylvania introduced an amendment to a war appropriations bill, aiming to prohibit slavery in any territory acquired from Mexico during the Mexican-American War. The amendment passed the House of Representatives but failed in the Senate, where Southern opposition was stronger. This unsuccessful proposal intensified sectional tensions and foreshadowed the deepening divisions over slavery that would lead to the Civil War (history.com).
