Which of the following was a major cause of the Civil War?

• A. Conflicts about tariffs and economies.
• B. States' rights issues unrelated to slavery.
• C. Disputes over whether the federal government could regulate slavery in western territories.
• D. Conflicts regarding the extension of slavery in new states.

Answer: (D)

The key issue here is whether slavery would spread into new territories and states. That question drove the fiercest sectional conflict in the United States, shaping politics, laws, and even violence in the decades before the war. Tariffs and economic disagreements did fuel tensions, but they didn’t mobilize the country toward war in the same way. Debates over who should decide the fate of slavery in western lands—federal authority versus popular sovereignty—made the stakes of expansion clear, leading to events like the fights in Kansas and major court rulings that polarized the nation. In short, the expansion of slavery into new states and territories created the irreconcilable differences that culminated in the Civil War, which is why this option best captures the major cause.