You ask a good question about violence in the United States, though it’s in large part a question about the American south and west, and about African Americans—the homicide rates of northern states are not much greater than those of Europe. It isn’t just guns, because even if you subtract all the killings with firearms and count only the ones with rope, knives, lead pipes, wrenches, candlesticks, and so on, Americans still kill at a higher rate than Europeans. ...
My own guess is that Americans (particularly in the south and west)
never really signed on to a social contract that gave government a
monopoly on the legitimate use of violence, as Europe did. Americans not
only retain the right to bear arms but believe it is their
responsibility, not the government’s, to deter harm-doers. With private
citizens, flush with self-serving biases, acting as judge, jury, and
executioner, body counts can pile up as trigger-happy vigilantes mete
out rough justice. This may be a legacy of the long periods of anarchy
in the mountainous south and frontier west, and of the historical
failure of the police and courts to serve African American communities.
--Steven Pinker, Freakonomics blog, on the where, how, and why of U.S. homicides