This document provides an overview of Key Concept 5.2 from the AP US History curriculum, which discusses the intensification of debates over slavery and other issues that led to the Civil War. It outlines the ideological, economic, and political differences between the North and South on the issue of slavery. Several attempts were made in the 1850s to resolve the slavery issue territorially, including the Compromise of 1850 and Kansas-Nebraska Act, but tensions continued rising. The election of Abraham Lincoln in 1860 on a platform opposing the expansion of slavery led to Southern secession, starting with South Carolina, and marked the onset of the Civil War.