>Where are the battle lines?

I think this is a pretty naive take and basically assumes that a second civil war would play out like the first. If we ever see a such a war, it won't be some guys from one walled off area fighting guys in a different area trying to win land. The battle lines won't be determined geographically. This will also definitely not be a conventional war like the first civil war. Such 40/60 places will not try to topple their neighbouring states for their own benefit, they'll be fighting among themselves. If you stir enough hatred, people will eventually clash in the streets. If you keep stirring, things might spill over to other regions. If this engulfs the entire US, you could have a full blown war without a single clear line of land along which people shoot each other. The lines will be determined by ethnicity, wealth, religion or a thousand other sources of conflict that are not so easily separated on a map.

It would look a lot more like Rawandan genocide.

I think we'd have to file that under "reasons to be optimistic" but it's a grim entry. A full-scale second civil war may be pretty damn near impossible for the reasons you mention, but on every other front than physical violence that war is being fought, actively, today - and as Dobbs has shown, it really can affect one's daily life.

We've seen plenty of street violence too: destabilizing and long-lived amounts of it, for example in the case of the CHOP zone in Seattle or the insurrection on Jan 6. You don't have to go looking to get affected.

EDIT: my Dobbs comment is going to seem glib and vulnerable to the obvious counter that courts make unfavorable rulings all the time - by definition one side loses. I meant that you can trace a pretty clear line from the abnormally intense political and cultural struggle that's been going on since ~2016 and the conditions that led the supreme court to make that decision (and make it in the way that they did.)