What was a main issue that caused sectionalism in the United States before the Civil War?

The issue of slavery was a central factor that caused sectionalism in the United States prior to the Civil War. This deeply divisive issue created distinct social, economic, and political differences between the Northern and Southern states. In the North, an increasing number of people were opposing slavery, leading to a growing movement for abolition and new ideas about civil rights. Conversely, the Southern economy heavily relied on slave labor for its agricultural output, particularly in the cotton industry, leading to strong regional support for its continuation.

These divergent attitudes towards slavery fostered distrust, inflamed regional identities, and created an atmosphere where compromise became more difficult. Legislative acts like the Missouri Compromise and the Kansas-Nebraska Act further exacerbated tensions, as they attempted to balance the interests of free and slave states, but often led to conflict and violence instead. Thus, slavery was not just a moral issue, but one that shaped the economic foundations and political structures of the two sections, leading to increased sectionalism and ultimately, the Civil War.