From Steven Pinker's The Better Angels of Our Nature, a passage relevant to the whole post-Newtown gun debate, and the reason for the higher incidence of violent crime in the US as compared to other Western countries. He quotes historian Peter Spierenburg's aphorism that "democracy came too early" to America:
In Europe, first the state disarmed the people and claimed a monopoly on violence, then the people took over the apparatus of the state. In America, the people took over the state before it had forced them to lay down their arms - which, as the Second Amendment famously affirms, they reserve the right to keep and bear. In other words Americans, and especially Americans in the South and West, never fully signed on to a social contract that would vest the government with a monopoly on the legitimate use of force. In much of American history, legitimate force was also wielded by p0sses, vigilantes, lynch mobs, company police, detective agencies, and Pinkertons, and even more often kept as a prerogative of the individual.