The document discusses the political and sectional tensions in the United States in the late 1840s and 1850s surrounding the issue of extending slavery into the new western territories. It summarizes that the 1848 Treaty of Guadalupe Hidalgo raised debates over the Wilmot Proviso which sought to ban slavery in the territories. Both major political parties, the Whigs and Democrats, advocated for the popular sovereignty doctrine to allow settlers in each territory to decide the slavery issue themselves. The Compromise of 1850 temporarily defused tensions through a series of measures, but the issue continued to divide the nation along North-South lines.