The term refers to the action of making slavery illegal or forbidden in a specific area or territory. In this context, it means that the legislation made it illegal to have slaves in any new territory acquired from Mexico after the Mexican-American War.
Related terms
Missouri Compromise: Legislation passed in 1820 that prohibited slavery above the 36°30' parallel line, ensuring an equal number of free and slave states.
Compromise of 1850: A package of legislation passed by Congress to maintain a balance between free and slave states, including the Fugitive Slave Act.
Kansas-Nebraska Act: An act passed in 1854 that allowed residents of Kansas and Nebraska territories to decide whether they would allow slavery within their borders through popular sovereignty.