The previous movie recommendation, Ride With The Devil, ties in with the idea that any coming conflict in America, really, at its core, will be nothing new. Just as the war in Missouri was truly brother against brother, neighbor against neighbor, and nobody, no matter how hard they tried, could not either be neutral or unaffected by the war.
Back almost twenty years ago, while knee deep in graduate studies for an incomplete MA in History, I was introduced to a great history on the guerrilla war that covered Missouri during the American Civil War. Inside War by Michael Fellman (here and here) is by no means the only or the best work on the conflict in Missouri. However, what stuck with me was the great use of primary sources, letters and diaries left by those who witnessed and were impacted by their experience. Most casual history buffs have heard of Quantrill and his raid on Lawrence, Kansas. Or of the brutality of "Bloody" Bill Anderson.
Fellman dives much deeper into the subject. He starts with an analysis of the society in Missouri in the 1850s and how the events in "Bloody Kansas" in the 1850s impacted Missourians. He puts forth the idea that while many Missourians were loyal to the Union, they were very troubled by the over reach of the Federals. Does this sound very familiar? The descriptions and opinions, nay, beliefs, towards each other were dehumanizing at best. Thus, atrocities towards each other could be defended. Again, does this sound familiar?
Thus, due to the extreme measures taken by both sides during the war, post war Missouri was marked by long held grudges between families and neighbors, with no apologies or forgiveness. I would argue that any coming conflict would have the same complexity of relationships.