What specific event do you think will cause americans to start killing each over the slavery

Bitterness and animosities around the issue of slavery, whether it should be allowed to exist or should it be abolished, accumulated for many decades in 19th-century American politics and federal life. The Union was divided into slave and free states, and their representatives often clashed in Congress over slavery-related issues. Very delicate and precarious balance was getting harder to strike.

The immediate cause, the spark that detonated the Civil War in 1861 was the election of an ardent abolitionist, Republican Abraham Lincoln as U. S. president. Some states seceded even before his inauguration and others after it. His election was the direct pretext for secession and the birth of the Confederacy.