What bad things could potentially happen if and when pro-slavery and antislavery groups begin to rush into popular sovereignty Kansas territory?

Killings and violence

Explanation:

Now that actually did happen. Groups of each moved into Kansas territory so they can make it either a slave or free state. It had so much bloodshed they had a little war called Bleeding Kansas. The two groups were both called Border Ruffians and they fought each other to gain the power.