Steven Pinker has an article
on how the rate of killing has tended to fall since prehistoric times. I would suggest that war just doesn`t pay no more, except, possibly in the case of mineral rich targets.
Warfare in medieval Europe used to go on in a desultory fashion with no end in sight because the stakes were low: one set of aristocrats felt they had the right to supplant another in collecting taxes from the peasants. (Dynastic marriages, so often seen as bringing peace in the short term, tended to create long-term situations in which every throne had multiple claimants with plausible genealogies.)
War couldn`t do much damage to the productive capabilities of rain-watered cropland, so why not fight? But once most of the value was in fragile buildings and the like, war became a lose-lose proposition.
At the level of crime, the Lily Burk case out in LA (see below) suggests just how many ways cops can build a case against a killer if they are really motivated to go all CSI on a bad guy. They`ve got security camera footage of the kidnapper and his victim pulling into parking lots, they`ve tracked her cell phone, they`ve got ATM records, etc.
I`ve never actually sat all the way through a CSI
episode, but I very much like the fact that lots of would-be criminals who watch those shows now believe that the police all have high tech hoodoo powers of detection so that they are more likely to believe crime doesn`t pay.