While slavery was certainly an issue, historians point to other issues involved in the Civil War. Such issues as how much control the federal government should have over states, industrialization, and trade had also created great tensions between the North and the South.
By 1860 when the South seceded, the nation was divided into two differing regions. While the South was primarily an agrarian area with people of British origin or of African origins, the North was an industrialized area with family farms, commerce, and transportation that brought in many people from Western Europe, especially Irish and German. As the population of the North grew, this section of the country gained influence in the national government, much to the consternation of Southerners.
In the 1850s with the rise of the Republican Party, the first party with no appeal in the South, the industrialized North and the agrarian Midwest became committed to the cultural attitude of free-labor industrialized capitalism. And, thus, the North began to oppose slavery. With dissension between the two areas of the country increasing from issues such as that of abolition of slavery which threatened the cotton industry, the South seceded, and the Civil War began. President Abraham Lincoln unbending attitude that the Union should be preserved was also questioned as unconstitutional. Nevertheless, he refused to allow the South to secede; the first shot was fired at Fort Sumter in 1861 and a war began that would cost over a million American lives.
Excellent answer! Of course, as Edward A. Pollard pointed out in A Southern History of the War (published 1866) the primary reason was economic exploitation of the South by Northern industrialists and the Federal government, largely centering on tariffs. Eighty percent of the income of the United States government came from export duties on agricultural products from the South. But import tariffs were extremely high, as a means of economic protectionism for industries in the North. This meant that, although superior products were available from Europe and were much less expensive than products from the North, after the import duties the prices were so high Southerners were virtually forced to buy tools and other products from the North. This simmered for decades, and the war almost broke out several times before the 1860s just from this issue. The protectionist idea was probably a good one in the 1790s, but by the 1840s was a serious drain on the Southern states' economies, and no longer necessary to protect industries in the North.
The States' Rights controversy was also a major issue, as the Federal government took more and more power to itself not specifically given to it by the Constitution. Although all such powers were guaranteed to the states by that document, the Federal government began accumulating further powers within the first few years of the new republic, a process which has continued to this day.
Slavery became an issue principally because of the troubles in Kansas and Missouri, caused basically by bandits claiming their actions were inspired by pro- and anti-slavery principles. But the triggering incident of secession was the election of Abraham Lincoln as president. Although the facts have become obscured, it seems some of the Electors (who are of course appointed, not elected) changed their votes from the way their states voted, and appointed Lincoln president. Since proceedings of the Electoral College were very difficult to find anything out about, whether true or not this was the deciding factor for South Carolina's secession.
Lincoln's position was that while the people had the right to rebel against the government if they felt that government to be oppressive, the states did not have the right to leave the union. I believe he was right, and that had the Confederacy remained North America would have become a land of several smaller countries, all continually at war(much like the Europe the American people had escaped from). As far as I've ever been able to determine it seems the South was right about everything but slavery, the moral issue. And, as Napolean said, "The moral is to the physical in war as three to one," and being morally in the wrong was as bad a disadvantage as the population and industrial might of the North.
The Civil war started over differences in the economies in the North and South. While the Northern states had begun to industrialize, the south relied on agriculture. Mainly the production of cotton and tobacco. The south's economy was threatened by the abolition of slavery, because having to pay workers would cripple their profits. When Abraham Lincoln was elected president the South feared that slavery would be ended and succeeded from the Union.
Other events that led to beginning of the civil war include: Bloody Kansas Massacre, Kansas/Nebraska Act, The Dred Scott decision, and the 3/5 compromise.