Sentence:  Whether modern, industrial man is less or more warlike than his hunter-gatherer ancestors is impossible to determine....One thing that is true, though, is that murder rates have fallen over the centuries, as policing has <WSD>spread</WSD> and the routine carrying of weapons has diminished. Modern society may not have done anything about war. But peace is a lot more peaceful. 
Meaning of the word marked with <WSD> tags:  To proliferate; to become more widely present, to be disseminated. (from 13th c.)