When people evoke 'Civil War', I have to ask Where? People are not wearing identifying uniforms or living in specific areas. I don't know what my neighbors believe and they aren't advertising their beliefs.
Most civil wars look just like that. The (first?) American Civil War was very unusual, and an outlier amongst civil wars generally, in that there was a fairly clear geographical delineation between the opposing forces, and there was even a difference in the military uniforms of the two sides.
Most civil wars don't look like that at all. The combatants on both sides either wear the uniform of the pre-war military, or civillian non-unifiom clothing, with no way to tell at a glance which side a given soldier is on; And there are people from the same street, or even the same household, fighting on opposite sides.
As a result, most people keep their heads down; Advertising your allegiance is asking for trouble.
And in most civil wars, most citizens don't take sides at all, unless forced to do so.