Here are some non-gun related mass murders for you to examine:
The oldest one listed happened in 2003, so well below your 20 year threshold.
Dude, did you REALLY waste time looking these up? Man, you are pathetic.
Point is, mass killing are RARE in countries that limit guns. You had to cover numerous countries over a decade to find as many mass shooting as the US has in a year.
I could live with one mass killing a decade.
I entered a phrase into Google and found one website with all that info.
The point is, despite your claims to the contrary, mass killings would continue without firearms.
But what would also happen is that at least 100k crimes would not be stopped each year by a citizen with a gun.
And the story I posted about the single mother killed with a shotgun and a machinegun shows that the criminals will still have their guns. Both of those are harder to hide and harder to smuggle than handguns. And a machinegun is much tougher to get. But the wholesale ban on firearms didn't stop the criminals from being armed.