As many American soldiers died in the Civil War as in every other war we've ever fought combined. If we were as divided now as we were then, I think it'd be surprising as hell.
The Civil War didn't occur just because of how deep the divisions were, but because they were strongly correlated with geography and not strongly correlated with class (particularly, that the divisions were quite present among the upper class with disproportionate influence on governments, and, while not perfectly aligned with geography, strongly correlated with it especially among the upper classes.)
The same degree of division with different geographic and class distribution could very well not have similar results.
