The author’s main point in this passage is _________.

The passage focuses heavily on one idea: the Civil War crisis was long-simmering. The entire first paragraph mentions many details that contributed to the climate of distrust and dissension between the North and South in the years leading up to the Civil War, going all the way back to the mention of the Mason-Dixon line’s establishment in the 1600s. The remaining paragraphs continue to discuss the climate in pre-Civil War days, focusing on the Dred Scott case and the isolation of the West.