I was watching a video about how up to world war 2, there was only a "shoot to kill" rate among soldiers of about 3%. Soldiers simply weren't shooting at the enemy. Most people aren't wired to.
Info about this is almost always traceable back to one source, "Men Against Fire" by Marshall, and the subsequent books he published and the various later books by other authors that primarily source his work. You might see Grossman come up as another name in this area, although he's writing much later and referencing Marshall.
This information is highly questionable. As this essay from
Robert Engen states:
Here, Marshall becomes extremely problematic as a source. Historians and researchers since the 1980s have been consistently demonstrating that Marshall did not have the evidence to back up his claims. Roger Spiller, among the first historians to publicly criticize Marshall, claimed that his ratio of fire numbers were ...an invention, and that Marshall had no use for polite equivocations of scholarly discourse. His way of proving doubtful propositions was to state them forcefully. Righteousness was always more important for Marshall than evidence.36 Other historians discovered that none of Marshalls aides and assistants could ever remember Marshall asking the troops questions during the group interviews that had anything to do with whether they had fired their weapons.37 In the surviving field notebooks used by Marshall during his interviews, historians have found no signs of the statistical compilations that would have been necessary to deduce a ratio as precise as that found in Men Against Fire.38 Such a precise, surprising number as the 15 to 25 percent ratio should have required a great amount of hard work and data-gathering to arrive at, but there is no evidence that Marshall carried out the statistical legwork his claims imply. The only interview notes actually located were found in an archive of a Maryland National Guard division, wherein soldiers testified to having used their weapons in action. There was no mention of the ratio of fire.39
In general, it also seems to be flying in the face of common sense. In 5000 years of recorded history, nobody thought to mention that only 1 in 33 people in a given battle will actually bother fighting.
The figure you mention here, 3%, is ludicrously low, and would imply that in WWII, an average engagement of one squad against one squad at close quarters in Stalingrad resulted in either nobody firing their gun, or everybody firing their weapon with the intention of missing. Should your squad be lucky enough to be gifted with one or, heaven forbid,
two soldiers willing to actually aim properly, you would presumably be at an enormous tactical advantage and win every engagement. Any other casualties in small arms battles would no doubt have come as a result of accidents, people tripping on rocks, or ricochets that mistakenly hit somebody after you aimed to miss. Now, Marshall or Grossman might say that in fact, the Soviets and Germans had sufficiently dehumanized the enemy blah blah blah, and that it was just the good natured Americans and Allied forces who were made of the stern moral stuff. This would be an even more problematic assumption, because it would mean that presumably while only 3% of Americans bothered trying to kill anybody, most Germans did. From which we could infer that the Allies couldn't possibly have won the war, since their soldiers were all comprised predominantly of people unwilling to kill.
The essay goes on:
Exceptions include when non-killers are in groups, when they are under authority, or when an opponent is running away from them, all of which were circumstances Grossman identifies as those in which normal individuals might overcome their resistance to killing. This list of exceptions is substantial enough on its own that one might reasonably question the effectiveness of this resistance, even by Grossmans standards.
WWI and WWII propaganda is famous, and you can trivially bring up outright racist posters about the Japs and the Huns and how people should be killing them. Dehumanization is as old as humans. Go kill those savages for the empire. Defend Christendom against the Moslem Turkomen. Now, this is not to say that everybody will be willing to kill. Reactions to battle are complex and it's frankly not a well studied area in psychology. But there was no line in the sand where in WWII, people were good and righteous and wouldn't kill, then fifteen years later they unlocked the secrets to bootcamp indoctrination and then after that we entered into the modern era of people being willing to kill en masse.