Good answer overall, but I am unsure about generalizing this to previous Japanese behavior in general. WW1 seems OK for German POWs. But I'd wager things looked crappy in the context of their occupation of Korea, which started in the 1890s, IIRC.

@ItalianPhilosopher WW1 and the Russo-Japanese War were exceptions due to Japanese ambitions about international recognition; the answer I linked explains this. Otherwise, Japanese conduct during the Boxer rebellion (which was not against European powers, like the other two conflicts), occupation of Korea, etc. all the way back to the 1592/7 invasion of Korea and war between different Japanese daimyos was reflective of how they behaved during WW2.

@o.m. I've already discussed the Kriegsgerichtsbarkeitserlass and how it relates to the question in my answer. The Einsatzgruppen I wouldn't consider "bottom-up", even if within them, some crimes were "bottom-up"; these were "top-down" death squads created for the express purpose of extermination. Obviously, they would collect the most sadistic and aggressive of individuals for service and were beholden to different "rules" than regular units. Unless regular Wehrmacht behaviour was comparable (which, overall, it wasn't), I wouldn't consider their actions "bottom-up".

If you back to 1592, I am pretty sure things looked beastly in Europe as well. cf. the 30 Years War in which some areas are claimed to have seen a 60% population drop... Colonial wars in the 19th century by Europe may not always have seen non-Europeans well-treated either. I don't disagree with you overall - that's why I cited Korea's occupation - but I'd just rather not see a blanket "Japan was fond of war crimes" statement and a bit more qualifications around that statement would make for a better answer

@ItalianPhilosopher I disagree. Naturally, the further back you go, the less "rules" will be observable in European warfare. That being said, the 30 Years War was the exception, not the rule; lasting a very long time and fuelled by religious hatred, it is not comparable to other conflicts. Not to mention that, again, the 30 Years War is remembered as such; it is remembered to have been particularly brutal, cruel, and savage. It was not, in any way, "the norm", while no such distinctions are made for Japanese warfare during the same periods. As for your second comment...

@ItalianPhilosopher I don't want to get into a drawn-out discussion in the comment section about this, but my claim was not that "Japan was fond of war crimes". The point is that the value of a human life was extremely low in Japanese society, for cultural, social and pure population reasons. The basis of Japanese philosophy, to serve, and to serve unwaveringly, without regard for one's own life or those of others, will inevitably generate an attitude that results in actions we now call "war crimes". Especially coupled with Japanese ideas of racial superiority and divine favour.

@Borealis, I could characterize it as encouragement "from the top" to come up with atrocities on the ground. Consider the Wannseekonferenz -- it took stock of what had already happened in different places, in different ways, and tried to streamline the genocide. Typical for the Nazi mix of setting goals, not methods.

"Any who refused were beaten severely by their NCOs." - this means that some did refuse. Are there cites for that in the book?

Discussions of war crimes always involves a certain danger of losing perspective. I moved this discussion to chat in response to a flag. Please ensure that further discussion remains within the bounds of scholarship.