The good news is that the vast majority of soldiers are loath to kill in battle.

Unfortunately, modern armies, using Pavlovian and operant conditioning have developed sophisticated ways of overcoming this instinctive aversion. The psychological cost for soldiers, as witnessed by the increase in post-traumatic stress, is devastating.

The psychological cost for the rest of us is even more so: contemporary civilian society, particularly the media, replicates the army's conditioning techniques and, according to Lt. Col. Dave Grossman's thesis, is responsible for our rising rate of murder among the young.

Upon its first publication, ON KILLING was hailed as a landmark study of the techniques the military uses to overcome the powerful reluctance to kill, of how killing affects the soldier, and of the societal implications of escalating violence.

Now, Grossman has updated this classic work to include information on 21st-century military conflicts, recent crime rates, suicide bombings, school shootings, and much more. The result is a work that is sure to be relevant and important for decades to come.