U.S. Civil WarWhy did the U.S. Civil War start?
The Civil War began on April 12, 1861 due to a breakdown between the relationship between the federal and various state governments. Although The Northwest Ordiance set up the process for statehood, it failed to address the issue of slavery. As a result by 1820 this flaw became increasingly dangerous with regard to the 'balance of power' in the Congress. It also began to polarize political opinions between the members of Congress, probably the most vocal was the Senator from South Carolina John C. Calhoun. Calhoun advocated 'nullification' the right for South Carolina to ignore any Congressional act that they considered oppressive. His speeches increased the tension between the growing 'sectionalism' of the southern states at the expense of the federal union. In an attempt to maintain the status-quo Congress passed several pieces of legislation between 1820-1854, however these actions could be compared to putting a band aid on a broken leg and expecting it to heal. By the 1860 election it was clear that if Lincoln was elected South Carolina would secede, which it did 12-20-1860. Lincoln's view was that the nation was a union of the people not the states, therefore no state had the right to secede from that union. It was this conclusion that Lincoln held throughout the Civil War. While it is true that slavery was an issue, and by 1863 became the moral cause for the war, it was not the central cause for the war. The Civil War was fundamentally rooted in whose power is supreme, the federal government or the state governments and it took a civil war to forever put that argument to rest.
I've heard it argued that the war began with the founding of Jamestown and Plymouth. From the beginning, we had colonies defined by their geography, weather, and colonists, which resulted in differing and eventually conflicting ideas of religion, philosophy, education, and economics. The South needed slaves; the North did not; this issue embodied all the differences between North and South, was debated as the country was founded in 1776, left unresolved, and erupted 80 odd years later. Indeed, right from the beginning, congress played a balancing act with admitting a free state with a slave state, starting with Vermont and Kentucky in the 1790's, but with westward expansion, the balancing act couldn't continue. The South correctly argued that their struggle was a "Second American Revolution;" they were breaking away from the North as all the colonies had broken away from England; they had voluntarily joined the Union and now were voluntarily withdrawing. Had the differences not included a moral or "Human Rights" component, perhaps we would have had a peaceful breakup and the CSA and USA existing today. The sad irony is that when the war began, slavery was in decline due to the South "industrializing" it's agriculture--machines had begun replacing human labor, were cheaper to maintain, and their use didn't have a moral component. Had technological development accelerated, or had statesmen deferred the the issue for 10 years, the slavery argument would have been moot.
The real question is why didn't it start much earlier. The country was essentially divided from the start, and it grew into two distinct sections by the late 1700s, early 1800s. As the South grew even more dependent on slavery and the North became more populous and industrialized, there wasn't any reconciling the interests of the two. The election of Abraham Lincoln in 1860 was merely the flashpoint. War had been inevitable for some time.
Another reason was the western expansion, as new states were admitted the North and South became entangled over whether the new state was a slave state or a free state. As mentioned by someone else the election of Lincoln, a Northern Republican over three Democratic opponents was the breaking point.
The United States was a nation divided into two distinct regions separated by the Mason-Dixon line. The two regions had separate economic systems (plantation vs industrial) and many qualities. Having two "Americas" was a recipe for disaster, espeicialy with admitting new states as free states or slave states. There was no question that each region felt threatened by the other.
The main and explicitly stated reason for the American civil war was the differences on issue of slavery. Southern states with their mainly agriculture base economy depended heavily on slave labour. In contrast, northern states were more trade and industry oriented. They were not dependent on slaves for their running their trade and industry. Therefore it was easier for them to tale a more humanitarian view and oppose slavery.
Apart from this explicitly stated difference over slavery, historians have indicated presence of other reasons also for difference between Southern and Northern states. People in Southern states led a luxurious life and were more tradition oriented. IN comparison people in Norther,states were more industrious, better educated and more amenable to change.