Bill:

I am thinking there is more a big cultural thing going on. The murder rate peaked at around 9.7 in 1933 then fell pretty steadily until it started to climb again in the 60s and stayed at high rate sort of near the 1933 rate from the 70s to the 90s.

The early part of the century saw the urbanization of the country. Mass immigration from Europe and mass migration from the South to the North and from other parts of the country to the West. We handled all that then comes the 60s and everything starts to go to hell again for about 20-30 years until we began to get a handle on it again.

Improved policing may be part of our culture getting a handle on the thing again.