Australia: Port Arthur massacre; National Firearms Agreement.
Canada: École Polytechnique massacre; gun control legislation after a few years.
New Zealand is outside of the twenty years rule, but the Christchurch massacre led to a similar effort.
All of these countries are Anglophone, majority white, historically Protestant, and generally similar to America in a lot of ways; politically, socially, historically, etc.
So why was there no similar effort after the Columbine massacre?
This question has been answered before multiple times, here is one example: