In contrast, most of the world seems to be demilitarizing today, with arms races becoming ever sleepier as inventiveness gets sidetracked into making cooler Powerpoints to boggle other laptop warriors.
I wonder if the rise in organized sports since 1865 has lessened the chances of a dust-up by absorbing and re-directing communal excitements. The Civil War more or less made baseball the national pastime (it gave soldiers something to do in army camps). On TV today, you could see a lot of extremely excited people in towns like Palo Alto and Tuscaloosa cheering on their young heroes on the football field.
Or maybe the decline in family size?
These aren't original theories, of course. I wonder how you could test them?