Of course it's POSSIBLE.

But do Americans WANT it?

It's my theory that more aggressive people self selected to immigrate to America; that it's part of our genetics

Then shouldn't the people of Australia be more violent than Americans?  Weren't their forebears criminals shipped from England? 

That's what Vizzini says in The Princess Bride so it must be true.

Jason, not just aggressive people, but religious people too.

Or do those go hand in hand?

Geege... sort of but no....  violent criminals tended to be kept in prison whereas non violent criminals tended to have the relocation option. Anectodal: it's common knowledge in the gay community that a much larger portion of the (male at least) population is MSM, and Sydney Pride is the largest pride festival in the world.

and yeah.. different groups self-selected to immigrate to america, but by aggressive I don't necessarily mean "aggressive"... but that the willingness to relocate is pretty fucking rare, ime.

I always took "willingness to relocate" to mean "less afraid about risk", not "proclivity to fight".

but "less afraid about risk" is a prerequisite to "proclivity to fight"...

Correlation, but not causation, right?

more like sets and subsets.... the latter being a subset of the former.