What mainly caused the Civil War?

[Torie]

The Civil War would never happened without the peculiar species of chattel being extant. Tariffs was just the excuse. The grand plan of the South was to secede and take over the Carribean, and maybe Mexico. Cuba was the first morsel on the agenda.

[Torie]

The slave trade had long since ceased by the time the Civil War had started.  It was banned until 1808 at the Constitutional Convention and then banned forever, punishable by death, starting January 1, 1808.  The Civil War didn't start until the 1860s.  That's 50+ years of time between when Bostonians and New Yorkers could make money on the slave trade.  Not to mention owning slaves was outlawed in nearly every Northeastern state even by the 1780s, nearly 100 years prior to the War.

The slave trade was not banned (slaves were still bought and sold as chattel); slave imports were, because Virginia and other worn out tobacco lands had a surplus (Washington used to bemoan his hoard of unproductive slaves with nothing to do), and wanted to increase the value of their chattel. The main goal at that point, other than banning imports, was to create more land for the surplusage of slaves to work, and that meant driving the Cherokee out of the deep South, which Jackson did. It was all about money, and in this case the commodity were slaves. If there is a hell, the whole lot of them reside in it.

[Torie]

Without slavery, there would never have been a Civil War, period. In addition, the South would not have fallen behind so acutely economically leading up to the Civil War (which was what precipitated it; the South realized it was now or never, and it turned out never because the South waited on decade too long). The South would have been more forced to live off productive industry. 

During the 1850's, in percentage terms, the US had the highest immigration levels in its history, before or since, and almost all of it went to north of the Mason Dixon line. The die was cast.