What were the causes of the US Civil War?

The American Civil War is often discussed as if it was a crusade on the part of the North to free the slaves in the South. While it is true that there was significant opposition from Southern states to the election of President Lincoln, who ran on an anti-slavery platform, it is not really true that the North opposed the South out of a great desire, on the part of the common people, for the abolition of slavery.
First, it is important to note that the Unionist soldiers who fought were, for the most part, not driven by a desire to eradicate slavery. The war was not fought, initially, as an attempt to defeat slavery in the South. However, in the South, the idea of having their slaves taken away was certainly a major cause of secession from the Union. Because the South had an economy built on plantations—particularly cotton—Southern whites could not see any way that an end to slavery would not completely bankrupt them. Moreover, as the United States expanded, Northern and Southern states clashed over the issue of slavery in new territories, with the question becoming increasingly heated by the 1850s. As such, Lincoln's election was the final straw that caused the secessions.
The Southern states also strongly believed in the rights of individual states to determine their own rules. Not only did they feel that the federal government should be forbidden to enforce emancipation upon them, they also believed that they were fully entitled to leave the Union if it was no longer working in their interests.
The issue of differing interests between the states had already been causing these issues about secession to brew. Because the economies of the North and South were based upon different systems—the North was driven largely by industrialized labor—there was a sense of cultural divide, while issues of external trade could cause contention, as they potentially benefited one group more than the other. The largely Republican North tended to take opposing political stances to the Democratic South, so the two groups were already primed to split up on the basis of conflicting interests before the Lincoln election divided them entirely.
The South had a powerful regional identity, while the North's identity was more tied to being part of the United States. This was another bone of contention between the two groups, and one of the reasons they did not understand each other.
When Lincoln was elected, the Southern states, in fear of being an underrepresented minority whose ideas about slavery would be swiftly overturned, declared their secession, and the war began.