The annexation of Texas to the United States and the gain of new territory by the Treaty of Guadalupe Hidalgo at the close of the Mexican War (1848) aggravated the hostility between North and South concerning the question of the extension of slavery into the territories. The antislavery forces favored the proposal made in the Wilmot Proviso to exclude slavery from all the lands acquired from Mexico. This, naturally, met with violent Southern opposition. When California sought admittance into the Union in 1849 as a free state, a grave crisis th ....