The Kansas-Missouri squabble beginning in the 1850’s left a lot of people dead. William Quantrill’s raid on Lawrence, Kansas in 1863 killed roughly 200 people.
And what's this about “white-on-white violence?” Do white-on-black or white-on-indian massacres rate lower on the moral scale?
That whole Kansas-Missouri border war, which started before the Civil War and got really blood-drenched during the Civil War, saw hundreds and hundreds of non-combatant people killed in savage guerilla attacks on towns and outposts.
Quantrill was certainly one of the more prolific killers at that time and place..