... I hold that in the present state of civilization, where two races of different origin, and distinguished by color, and other physical differences, as well as intellectual, are brought together, the relation now existing in the slaveholding States between the two, is, instead of an evil, a good–a positive good.
The Missouri Compromise led to the Civil War because the controversy over Missouri's rights to hold slaves deepened the split between the North and the South. Also, when Kansas-Nebraska Act repealed the Missouri Compromise, the nation was irrevocably pushed to war.
Mexican-American War (1846-1848)
James Tallmage Jr.
The Nullification Crisis led to the Civil War because it made sectionalist ideas in the country exacerbate and prompted John C. Calhoun to resign from his post as vice president, adding to the social unrest.
Uncle Tom's Cabin (1851)
John C. Calhoun
Uncle Tom's Cabin
John C. Calhoun's statement of "Slavery - A Positive Good" led to the Civil War because it addressed the essential cause of the Civil War - slavery - in a drastically pro-slavery way, which further divided the nation.
Kansas-Nebraska Act (1854)
This would work out great for my railroad
Popular sovereignty, great thing, ya know!
The Mexican-American War was triggered by Texas Annexation and ended with victory on the U.S. side, with Mexico ceding a huge tract of land on the Western Coast to the U.S. It led to the Civil War because it potentially added slave-holding territories to the nation and spurred sectionalist ideas on Manifest Destiny to diverge even more.
The publication of Uncle Tom's Cabin led to the Civil War because it was the first influential work of literature to present slaves as humans and thus stimulated the anti-abolitionists to act against it, intensifying the conflict.
Harriet Beecher Stowe
Kansas-Nebraska Act led to the Civil War because it basically repealed the Missouri Compromise and made slavery possible even above the 36º30' parallel, triggering both abolitionists and anti-abolitionists to act up and start fighting in Kansas.