Umm, none? Are you asking how often they are divided in their decisions? As often as the matters are ideology-driven: conservative vs liberal.
And if Democrats try to pack the Supreme Court with additional justices, then again: civil war.
And if Democrats try to pack the Supreme Court with additional justices, then again: civil war.
Why do you specifically call out Democrats here? The most recent court size increase was during the presidency of Grant, a Republican.
Anyway, regarding the original topic of the National Popular Vote compact, the Constitution does not specify how each state chooses its electors in the Electoral Collage. Initially, most state legislatures chose their electors without any popular vote at all!
Eventually all states switched to a popular vote system, individually, but this took several decades to occur. That initial switch seems more substantial than what is proposed in the National Popular Vote compact, so why are you confidently proclaiming that it would result in a civil war?
Who would raise an army to try and stop this? Who would be a willing foot soldier (besides you)?
Please, back up your bluster with something sane, something real, not just your personal nonsense. Otherwise? STFU.
The constitution and founding fathers called for the exercise of the second amendment whenever the government went rogue, like trying to change the constitution, such as the electoral college, which ensures representation of minority populations, like farmers and other hands-on workers.