Oh good grief we could really go really deep into this discussion if you want too.
But since you asked..........
The Civil War was caused by a myriad of conflicting pressures, principles, and prejudices, fueled by sectional differences and pride, and set into motion by a most unlikely set of political events.
At the root of all of the problems was the institution of slavery, which had been introduced into North America in early colonial times. The American Revolution had been fought to validate the idea that all men were created equal, yet slavery was legal in all of the thirteen colonies throughout the revolutionary period.
Although it was largely gone from the northern states by 1787, it was still enshrined in the new Constitution of the United States, not only at the behest of the Southern ones, but also with the approval of many of the Northern delegates who saw that there was still much money to be made in the slave trade by the Yankee shipping industry.
Eventually its existence came to color every aspect of American life.
At the Constitutional Convention there were arguments over slavery. Representatives of the Northern states claimed that if the Southern slaves were mere property, then they should not be counted toward voting representation in Congress.
Southerners, placed in the difficult position of trying to argue, at least in this case, that the slaves were human beings, eventually came to accept the three-fifths compromise, by which five slaves counted as three free men toward that representation. By the end of the convention the institution of slavery itself, though never specifically mentioned, was well protected within the body of the Constitution.
It seemed to Thomas Jefferson and many others that slavery was on its way out, doomed to die a natural death. It was becoming increasingly expensive to keep slaves in the agrarian society of the south. Northern and Southern members of Congress voted together to abolish the importation of slaves from overseas in 1808, but the domestic slave trade continued to flourish. The invention of the cotton gin made the cultivation of cotton on large plantations using slave labor a profitable enterprise in the deep South.
The slave became an ever more important element of the southern economy, and so the debate about slavery, for the southerner, gradually evolved into an economically based question of money and power, and ceased to be a theoretical or ideological issue at all. It became an institution that southerners felt bound to protect.
