On the other hand, though, the war threatened to hand national power to slave owners, perhaps forever. As U.S. troops pushed far into Mexico, horrified Northerners realized that if the nation kept the land it was rapidly conquering, the South could create enough new slaveholding states to overwhelm the northern states. With troops still in the field, Whigs in particular, and Northerners in general, demanded a law that would prohibit slavery in the new lands.
