This dissertation argues that the gendered and sexualized popular discourse surrounding the crisis over the extension of slavery into Kansas Territory in the 1850s was central to changing northern public opinion in the antebellum political contest over slavery. Gendered (meaning the historically specific social and cultural ideas about what men and women should say and do) and sexualized (historically specific ideas, words, and actions having to do with sex and sexual bodies) ideology significantly influenced the political realignments of the 1850s. I examine the outpouring of northern popular literature produced about Kansas between the introduction of the Kansas-Nebraska Act in 1854 and the presidential election of 1860. In thousands of novels, newspaper articles, plays, poems, prints, and pamphlets, northerners presented a boldly gendered and sexualized critique of the political crisis over slavery in Kansas. Personifications of Kansas Territory as a white female, references to alleged rapes of free-soil northern white women by pro-slavery men in Kansas, images of the figurative rapes of free-soil northern white men by pro-slavery men, and attacks on the masculinity of northern "doughface" Democrats were influential in swaying northern popular opinion on the expansion of slavery, political party affiliation, and voter decision-making. The gendered and sexualized discourse about Kansas in popular literature served a crucial political function, as it fueled widespread northern commitment to stopping the spread of slavery, inflamed white northern animosity toward the South and pro-slavery men, and pushed white northerners who were previously unmoved by the issue of slavery toward supporting the free-soil Republican Party. By engaging with the historiographies of antebellum politics, antebellum gender and sexuality, nineteenth-century popular and print culture, and the Civil War, this dissertation presents a new and persuasive explanation for why millions of white northerners rallied in the late 1850s in opposition to the extension of slavery and in support of the new Republican Party. The gendered and sexualized discourse about the political crisis over slavery's expansion into Kansas was fundamentally decisive in the political realignments of the 1850s and the turn toward civil war.