How does the outcome of the 1846 Mexican War lead on to the Civil War? Click-on: Learn answers by reading these chapters in the History Book: Chapter 118. War Breaks Out With Mexico Chapter 122. The Wilmot Proviso Is An Existential Threat To The South Chapter 136. The Treaty Of Guadalupe Hidalgo Ends The War With Mexico Chapter 142. Salmon Chase’s New “Free Soil Party” Portends America’s “Third Political System”