I’ll put it forefront that I argue the Civil War was caused by the polarization of the country, sectionalism. The Wilmot Proviso from the Mexican-American War is seen by many as the “first round” to the political conflict. Another major event was The Compromise of 1850, which admitted CA as a free state as decided by popular sovereignty, established a Fugitive Slave Law, and forbade slave trade in D.C. However, this fugitive slave law was often resisted by antislave and abolitionist Northerners, ultimately driving a wedge between the North and the South. Lincoln also addressed the writer of Uncle Tom’s Cabin, Harriet Beecher Stowe, as “…the little woman who wrote the book that made this great war,” as this look made tons of northerners abolitionists; I recommend looking into it. Another major event was the Kansas-Nebraska Act leading to “Bleeding Kansas.” Also John Brown’s Raid at Harpers Ferry causing southerners see the raid as proof of the north’s intentions to use slave revolts to destroy the south. There’s a lot of events but I hope this gives you a starting point.
The Wilmot Proviso was a piece of legislation proposed by David Wilmot (D-FS-R PA) at the close of the Mexican-American War. If passed, the Proviso would have outlawed slavery in territory acquired by the United States as a result of the war, which included most of the Southwest and extended all the way to California.
Wilmot spent two years fighting for his plan. He offered it as a rider on existing bills, introduced it to Congress on its own, and even tried to attach it to the Treaty of Guadalupe Hidalgo. All attempts failed. Nevertheless, the intensity of the debate surrounding the Proviso prompted the first serious discussions of secession.
