Name the events in may 1856 that further inflamed the slavery issue?

In May of 1856, several violent events further inflamed the United States in respect to its ongoing slavery/anti-slavery tensions. The first (on the 21st) was an attack on the town of Lawrence, Kansas, by a large group of slavery advocates: great damage was done to the settlement and one citizen was killed. This attack was apparently motivated by a (non-fatal) shooting during the previous month; it also served as a motivation in turn, with five pro-slavery Kansas settlers being killed in retaliation just a few days later (on the 24th).