@Setanta,
I think I've said about ten times now is I think it's a mixture of things - most importantly that there is easier availability to guns in the US
You should read that stuff about the psychology of killing - only substitute the word 'bullying' for 'killing'- you might find it applicable to your own behavior.
For about seven years now you've followed me around maligning my character and intelligence, usually calling me derogatory and debasing names (not this time I admit), all without ever having to look me in the eye - even when I told you I'd meet with you and your girl to have it out.
No - you'd rather keep your safe and anonymous distance to debase me as a human being.
I don't think Americans are genetically more predisposed to violence, but I do know guns are more readily and easily available - which is especially dangerous given certain tensions that are the reality in our country, borne out by our history, as opposed to certain other countries - namely Canada.
Do I have to say it again? I do not believe it is because there are more people - but I do believe it is because there are more guns, and more historical and racially based tension than might be present in other countries.
I think it is complicated - but just as I don't believe black people or any other race or nationality of people are more genetically prone to violence, I don't believe Americans are either.