I have honestly found myself thinking about this on occasion.
First there are all the people who post in several places claiming they are convinced a civil war is coming. Usually these show up in topics where various posters are arguing and maybe flaming each other.
Second you have the changes in how the two political parties, Republicans and Democrats, treat each other. Not just the politicians but also the citizenry who consider themselves loyal to their party despite anything that comes or is revealed about their team.
Third is all the open hostility I sometimes encounter in real life.
Fourth I will admit one comment I saw, a non-nasty actually funny one, about a Media Civil War got me thinking how the various technologies would factor in.
If such an event happened what would it be like?
Do we fight through programs and console systems instead of actual combat, racking up virtual kills over real ones?
Should verbal insults through various media take precedence?
I do not think the old North vs. South divide shall repeat itself but how would a divide occur?
If along geographical lines, where are the divisions likely to happen?
Are more than two sides possible?
Or does the divide lay more along political lines thus causing problems in a more widespread area?
It may be a long time before I figure out any possibilities and answers to these questions.