The social sciences used to have their own forums in PF, what happened to them? They used to be a great lace for discussion. Anyways, this still seems the best place to ask this question. According to Wikipedia at least, the homicide rate in the U.S. per 100,000 persons increased from about 1.2 to 4.6 in the first decade of the 20th century. It looks like the most dramatic increase was during the years 1905 to 1907, where the rate went from 1.3 in 1905 to 4.9 in 1907. It looks like before that period U.S. homicide rates were fairly on par with the U.K., with rates barely over 1, but after that period U.S. homicide rates never again fell bellow 4. Is there a theory on why the sudden increase at that time specifically?