In Chapter 4, Kearns Goodwin discusses the Mexican-American War and the controversies surrounding it. Many Whigs and proto-Republicans opposed the war. Lincoln supported a Congressional resolution against the war and defended his antiwar stance, even at the risk that it would harm his political aspirations. Bates also opposed the war on the grounds that it was “part of a conspiracy to extend the reach of slavery” (123). Both Seward and Chase expressed reservations about the war but stopped short of publicly opposing it out of fear of the repercussions for their political careers. As Kearns Goodwin notes, “Manifest Destiny was in the air” (122), and the majority of Americans supported the war as a way to expand the nation’s territory.

As Bates’s position shows, the issue of slavery was inexorably tied up in the war. Seward, Chase, and Lincoln supported a ban on slavery in any new territories. Bates also supported the ban, known as the Wilmot Proviso, but on different grounds; he believed that if Southerners brought slaves into the new territories in large numbers, it would deter free whites from settling there, “thereby precluding growth and progress in the region” (124).

The war coincided with the 1848 presidential elections; as a result, the war and the expansion of slavery became central issues in the election.