Even before the Mexican War ended in 1848, the question of whether to allow or prohibit slavery in new western territories threatened to rupture the Union. Slavery’s extension to new states could give the slaveholding South a majority in the Senate; its prohibition would favor the North. To balance sectional interests, Congress passed a series of bills known as the Compromise of 1850. California, with a burgeoning migrant population, was admitted to the Union as a free state. Concessions were simultaneously made to slave powers, raising fierce debate.