I don't disagree that with your premise, and you can certainly see the Civil War as "Roundheads vs Cavaliers, round 2". But you can also see it starting in 1619 (first enslaved Africans arrive in the US) or 1640 (John Punch legally enslaved in one of the first legal decisions to distinguish between black and white races.) Or 1502 (start of the atlantic slave trade). Or further back (the muslim invasion of west africa.)
And trying to put an end date on the Civil War. Well. I mean. You only have to look at all the battle flags flying to see that it is clearly ongoing.
It isn't just the American Civil War. Any war is, to some degree, without beginning or end.