How did popular sovereignty lead to violence in Kansas?

Senator Stephen Douglas of Illinois wanted to encourage people to live in the west territories that were created by the Kansas-Nebraska act. In these territories popular sovereignty was used to determine the issue of slavery. Settlers that came to the new territories would be allowed to vote if slavery would be allowed.

Both territories were North of latitude 36.30, and according to the Missouri compromise, slavery was banned in the territories north of this line. the Kansas-Nebraska act would cancel the Missouri compromise. This caused some of the Northerners to feel betrayed by Douglas.