I've already mentioned the book titled On Killing - The Psychological Cost of Learning to Kill in War and Society by Dave Grossman (Lt. Col. of US Army). It gave some food for thought and I'm planning to write some of my speculation.

But what did the author write? Let's summarize.
He starts with the observation that most men has a natural resistance to kill (only 2% of men - those who have "predisposition toward aggressive psychopathic personality" - can go on killing without becoming a nervous wreck). This resistance is so high that even at times that our life is directly threatened (like others shoot at us) still difficult to overcome it. This resistance is the reason why infantry fire was so embarrassingly ineffective in the past 300 years - with the exception of machine guns - despite the fact that infantry weaponry (rifles) are reliable and accurate enough to cause massive losses among the enemy.
The author gives examples and sources, such as a Prussian experiment in the late 18th century, several reports and notices from several authors during 19-20th centuries (American, French, Israeli etc.), and an interesting work by a US Army historian who (and his coworkers) made mass interviews with fighting GIs during and after WWII. Also he cites his own conversation with veterans of WWII and Vietnam.
He gives new ideas on what's really happening on the battlefield. He compliments the widely known fight-or-flight model with two other options: in reality the soldiers can fight, posture, submit or flight. And most soldiers choose the second option.
Then he ponders on what enables killing (I'm gonna write more about this later) and how modern (post-WWII) armies achieve this. Then he compares these methods with the ways of contemporary mass media. His conlcusion is (after pointing out the exponential rise of violent crimes) that mass media has an undesirable effect on society.

What interesting for me is this resistance, and the enabling part. These things are actually give an entirely new way of looking warfare, and how and why battles were won.
For example the part officers (the demanding authority to kill) play in the enabling. When people (professional historians, history pros and other armchair generals) comparing the Hellenic phalanx with Roman manipulus and why the latter was more successful they compare everything but the officers. In the phalanx he's only one among those who stand in line and do the poking with pikes, but a Roman officer is one outside the formation and pressuring the soldiers to kill. It makes a huge difference if someone shouting in your ears "stab! stab! stab!" and generally pressuring you to kill. Especially if this one person is an exemplary one, a veteran whose skill in killing surpasses all the others in that particular unit. However noone talks about this because noone thinks about it.

I'll continue this sometimes, maybe only next weekend, we'll see. If you wish to read the book you can probably find it on libgen.