It happened when the Nation was divided over slavery and other issues, i.e. industrial economy, Federal powers vs. State, etc.; and all the pieces fell into place at one time.
Are we that divided yet? Maybe, IMHO. At least we are well on the way, judging by the count in the last election and animosity between the sides.
This time could be uglier than then as we don't have the luxury of cleanly dividing the sides with geographical lines which enabled our forefathers at that time to hold the bloodshed of non-combatants to a minimum.
One thing for certain, adding 8mil.-12mil. (x 5 including family members) further complicates the issue with unpredictable results.