Why was another compromise thought to be necessary in 1850? Southern Democrats forced the issue of northern obstruction of "slave catchers" hunting down runaways, especially in the border states of Illinois, Indiana, Ohio, and Pennsylvania, demanding that slaveholders' rights to the return of "stolen" property be respected in states where slavery was illegal. The Oregon, Utah, Minnesota, and New Mexico territories were about to vote in favor of slavery, which antislavery northern congressmen would not allow. The Compromise of 1820 preserved a numerical balance between the number of "free" states and "slave" states, and the addition of new states and territories after the Mexican War compelled a return to the issue of numerical parity between North and South. 4