flea

The North's original name for the conflict was the War of the Great Rebellion, while the South called it the War Between the States. As others have said, it goes back to the essential question that started with the Articles of Confederation: is the United States one nation, indivisible, or a collection of independent states? The Southern colonies were generally on the states' rights side of the question. When Jefferson made the Louisiana Purchase, he threw a continent-sized wrench into the machinery, since any new states were not sovereign colonies in the sense of the original 13 states. Slavery became the fracture point because of the question of whether the new states would allow slavery, banned in the North. The question was fought in Congress; in the courts; and in bloody Missouri and Kansas. It probably would have been fought state by state to California without the Civil War.

Lincoln would probably have tried to continue to compromise, if the Confederacy hadn't fired on Fort Sumter.

I don't think anyone imagined it would last so long or be so ugly, although I suspect Lincoln and Lee had some sense of it. At the beginning, Northern volunteers poured it saying it would be a "breakfast spell" -- they'd whip those Southerners and be home by dinner.