"The US is around average of all nations in both categories."
Very interesting. It's like God (or nature) requires a certain amount of killing.
Please, don't flame me, it is just an idle observation.
There is still quite a bit of variation, even if you add the two rates together. No where near as much as separately, but still, quite a bit.
I think culture and availability of resources has something to do with it.
It has been a few years since I compiled a list of the combined rates, so I can not give you the specifics. I think Britain or Germany had one of the lowest combined rates.
Another thing to consider is how accurate the reporting is. While murder and suicide both leave a body, it is easy for one to be reported as the other, if authorities are sloppy or bribable.