We know who the militia existed to fight.

The term "well-regulated milita" predates the constitution and traces back to the days when white people were often a substantial minority compared to the populations of enslaved black people they lived among.

On St Croix where a young man named Alexander Hamilton grew up, the ratio was 1 free person to 8 slaves, so the well-regulated militia was to assemble at the fortress if they heard a blast of the cannon: they were required to come with their weapons in order to put down a slave revolt.

Source: Alexander Hamilton by Ron Chernow.

It's also probably worth mentioning that "people" in "the right of the people" certainly excluded slaves from the right to own weapons, making the text even more burdened by its own history

My point is: what the founders understood was that some gun violence was the unavoidable cost of maintaining the system of slavery, itself a system of formalized/normalized political violence.