Even though we're in the north, I think we should have slavery.
Election of 1860
Kill them all!
The Kansas-Nebraska Act was the biggest cause because territory in the North was open to becoming a slave state. This directly violates the Missouri compromise. The Whigs were split into Republicans and Democrats.
Fugitive Slave Act
The Election of 1860 is the second biggest cause because Abraham Lincoln won the election, which caused South Carolina to secede from the Union. Other southern states soon followed in South Carolina's footsteps soon after.
Bleeding Kansas was a direct response to the Kansas-Nebraska Act. This was essentially the testing ground for the civil war.
The Fugitive Slave Act allowed Southerners to recapture their escaped slaves. This would have angered abolitionists because it made it harder to keep slaves safe from harm up in the North. Northerners could have even been hurt or killed in the process of recapturing a slave.