What caused the American Civil War? It is amazing that even today, over 130 years after the Civil War started, there is passionate debate regarding the "cause" of the Civil War. Consider this:
It is a fact that when the armies for the North and South were first formed, only a small minority of the soldiers on either side would have declared that the reason they joined the army was to fight either "for" or "against" slavery.
However, equally true is the statement: "Had there been no slavery, there would have been no war. Had there been no moral condemnation of slavery, there would have been no war." (This was made by Sydney E. Ahlstrome, in his monumental study of religion in America A Religious History of the American People, Yale University Press,1972, on p. 649)
The message here is that the reasons a nation goes to war are usually various and complicated. The American Civil War is no exception.
The curious thing is that although slavery was the moral issue of the nineteenth century that divided the political leaders of the land, the average American had very little interest in slaves or slavery. Most Southerners were small farmers that could not afford slaves. Most Northerners were small farmers or tradesmen that had never even seen a slave.
But political leaders on both sides were very interested in slaves and slavery. The South's economic system was based upon cotton--and slavery. The political leaders of the South, such as Robert Barnwell Rhett of South Carolina, William Lowndes Yancey of Alabama, The Fire-Eatersand Robert Augustus Toombs
of Georgia, recognized that if the South lost her slaves (i. e., had to pay slaves wages similar to what white laborers were paid), her entire socio-economic system would probably collapse. Hence any political action that took place that threatened the slavery system of the South received the undivided attention of the South's political leaders, many of whom were themselves slave owners.
Political leaders in the North were much more divided about the slavery issue. Many of the powerful abolitionists, such as William L. Garrison of Massachusetts, were either religious leaders or newspaper editors. A fewer number of abolitionsits, such as Senator Edwin Sumner of Massachusetts and Salmon P. Chase of Ohio, were politicians. The north had equally powerful political leaders such as democratic Senator Stephen A. Douglas who were either indifferent towards or supportive of slavery.
Today we recognize slavery as a moral issue. But in the early nineteenth century, it was seen as an economic issue first, moral issue second. A series of legislative actions, most notably the Missouri Compromise of 1820, had been enacted by Congress to put limits on the propagation of slavery, but compromise with northern and southern interests was always kept in mind. The South had an economic interest in the spread of slavery to the new territories so that new slave states could be created and the South's political influence would remain strong. The North had an interest in limiting the spread of slavery into the new territories for both purposes of controlling Southern political power AND support of the moral issue.
Up until the middle 1800s, slavery was kept as a background issue that remained largely the concern of political leaders of the South, and abolitionists of the North. But in 1854, the Kansas-Nebraska Act, sponsored by Democrat Stephen A. Douglas, brought slavery to the forefront of national attention. Kansas-Nebraska eliminated the old Missouri Compromise (which in 1820 had designated areas of the new territories in which slavery could and could not be introduced) and made it possible for slavery to be introduced in virtually any new territory. Douglas called the concept of allowing residents of the territories to decide the slavery issue for themselves Popular Sovereignty. Kansas-Nebraska caused a firestorm to errupt in the North, awakening many people to the danger of the potential spread of slavery. Moderate politicians such as Abraham Lincoln became active in the cause of fighting both the Kansas-Nebraska Act and the spread of slavery.
Although the majority of the American people-- including many moderate politicians like Abraham Lincoln--wanted to avoid Civil War and were content to allow slavery to die a slow, inevitable death, the most influential political leaders of the day were not. On the southern side, "fire-eaters" like Rhett and Yancey were willing to make war to guarantee the propagation of their "right" to own slaves. On the northern side, abolitionists like John Brown and Henry Ward Beecher of Connecticut were willing to make war in order to put an immediate end to the degrading institution of slavery.
These leaders, through either words or action, were able to convince the majority that it was necessary to go to war, and in order to convince them they justified the war with arguments that only indirectly referred to the subject of slavery (i.e., state rights et. al.).
Southern politicians convinced their majority that the North was threatening their way of life and their culture. Northern politicians convinced their majority that the South, if allowed to secede, was really striking a serious blow at democratic government. In these arguments, both southern and northern politicians were speaking the truth--but not "the whole truth." They knew that to declare the war to be a fight over slavery would cause a lot of the potential soldiers of both sides to refuse to fight.
So-was the war about slavery? Absolutely. If there had been no disagreement over the issue of slavery, the South would probably not have discerned a threat to its culture and the southern politicians would have been much less likely to seek "their right to secede." But was it only about slavery? No. It was also about the constitutional argument over whether or not a state had a right to leave the Union, and--of primary concern to most southern soldiers--the continuation of antebellum southern culture. Although the majority of Southerners had little interest in slaves, slavery was a primary interest of Southern politicians--and consequently the underlying cause of the South's desire to seek independence and state rights.
This has been my attempt at providing a brief, balance answer to a complicated subject which has been the subject of many books. For further reading, I suggest Kenneth Stampp's Causes of the Civil War.