What was the most important issue that separated the South from the rest of the nation?

the increase of immigrants to the region

slavery

desire to have cheap or free public land

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The correct answer is slavery. Slavery was the most important issue that separated the South from the rest of the nation. Southerners felt that the abolition of slavery would destroy their region's economy which primarily relied on slaves working in plantations. Northerners on the other hand held that slavery should be abolished for moral reasons. This issue deeply divided the nation.