I am saying the civil war would be short because only one side would have weapons

One side has weapons? Democrats don't own guns? Also is the military going to not be involved? You sound like you don't understand the complexities of politics and war. Because I don't care what political affiliation you are, if anyone says a civil war will be quick. Doesn't know what they are talking about.

As for regulation it is tricky. Weapons are a second amendment right to protect against a tyrannical government,

Weapons, particularly guns. Aren't a second amendment right. The right to organize a militia is.

however there are many mentally ill people who do not care about consequences to themselves or others, and we need to make sure they are helped, as well as don't have access to the means to inflict damage on society

What does that have to do with stopping mass shootings?