The causes of the Civil War

On the 150th anniversary of the start of the Civil War, I have been thinking about its causes.

It seems clear to me why the deep southern states seceded. Whites who benefited from slavery as slave holders or slave renters or who hoped some day to benefit from slavery help power and failed to recognize that slavery as they knew it was on the way our worldwide. They knew that other states had considered secession, and that nullification of federal law had not worked. And they radically underestimated the will of the northern states to preserve the union, they overestimated the military power of the Confederacy as compared to the Union, and they radically underestimated the pain that the Civil War would cause and the disruption of their lives, economies and societies that would follow its loss.

Why did the northern states go to war rather than allow the southern states to secede?

• They too underestimated the opponents military prowess and the pain of the war. 
• There were immediate economic interests threatened by the secession, such as tariff free access to cotton for the northern mills, loss of southern markets for northern goods and services, and loss of business for northern own shipping.
• Some were willing to fight to abolish slavery, some simply disliked the southern leaders for their culture and behavior.
• The northern states were economically successful and the electorate understood that they had better lives and more hope for the future than their peers in other nations; they attributed that condition importantly to their democratic republican form of government. It was unique in the world, and attempts to replicate democratic rule such as the French Revolution and the revolutions of 1848 had failed. If secession succeeded and the Union failed, they feared the loss of their form of government and thus the prosperity of their future. Indeed, many had an ideological commitment to the preservation of the democratic republican form of government as "a beacon to the world".
• The reduced Union would be vulnerable to attack by European powers, which might well combine with the Confederacy.

People on both sides saw the future prosperity of themselves and their families tied to the expansion of their "state" into the west from which the Native Americans could be eliminated as they had been in the east. They believed that the Union as constituted in the 1850s could come to dominate North America from sea to sea, from the Canadian border to the Rio Grande.

Southerners saw the expansion of slavery into the west within the Union as a dead letter with the election of Lincoln. The probably recognized that the rise of Republican power spelled the eventual emancipation of slaves and end of slavery within the Union.

Northerners could see that if the Union were weakened by the departure of the southern states then there would be a free-for-all for the west. The French took over Mexico during the Civil War and would be a competitor for empire in the West. Britain was not the ally it is today, and would be a likely competitor for the West seeking to expand the Canadian border south. Russia held Alaska (until 1867) and might seek territories in the West. And of course the Confederacy would  be an important rival itself, already including Texas. Allowing the southern states to secede might result in loss of the West and a permanent secondary status for the remainder of the Union.

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