Gun Control & RKBA

To clarify, of course there are mass killings, ISIS and Boko Haram notable offenders, and the lunatic in Norway certainly fits the profile, but the US is experiencing them with depressing frequency.

There is violence in every country. Northern Ireland and South Africa were both scenes of horrific violence, but in both countries the violence subsided after the causes for the violence were settled. Israel/Palestine is also the scene of terrible violence, but again, there is a specific conflict that causes the violence. Other than extreme inequality, there seems to be no specific reason for the violence here.

As to population, I am not aware of any studies linking population levels to violence. Both Australia and Canada are quite similar to the US in that:
all three countries are nations of immigrants, and all three countries were founded by British settlers, the Quebec area excepted. Given the similarities, what explains the remarkable difference in gun violence levels?