History: American Civil War (1861-1865)

Causes of secession
The Abolitionist movement in the United States had roots in the Declaration of Independence. Slavery was banned in the Northwest Territory with the Northwest Ordinance of 1787. By 1804 all the Northern states had passed laws to abolish slavery. Congress banned the African slave-trade in 1808, although slavery grew in new states in the deep south. The Union was divided along the Mason Dixon Line into the North (free of slaves), and the South, where slavery remained legal.
Despite compromises in 1820 and 1850, the slavery issues exploded in the 1850s. Lincoln did not propose federal laws against slavery where it already existed, but he had, in his 1858 House Divided Speech, expressed a desire to "arrest the further spread of it, and place it where the public mind shall rest in the belief that it is in the course of ultimate extinction." Much of the political battle in the 1850s focused on the expansion of slavery into the newly created territories. Both North and South assumed that if slavery could not expand it would wither and die.