The psychological technique of training soldiers to see the enemy not as a human being, but as a target, is relatively new. In other words, in past times many soldiers had a harder time killing one another due to a number of factors not the least of which was empathy.
Fascinating read and very enlightening. There’s also a theory to explain why so many muskets have been found loaded multiple times as well. Soldiers, at least some, would simply keep loading cartridges into their gun rather than shoot at the enemy. They’d seem like they were doing their job during all the noise and confusion but just did not want to fire at other people.