I think the war between China and Japan was always quite a traditional and age old war, the modern China vs Japan war started early in the 1930's I think, but historically they had been warring for many centuries. So it wasn't really included in the official scope of WW2, but I might be wrong on that. I rarely see it mentioned though (also I rarely see the Finish/Russian war mentioned even though it was an incredibly important stage of the overall war).
Geologically the feud between Japan and China was fairly unimportant for the Western world, which is why it probably isn't had so much weight put on it from education. It didn't really affect our economy, nor did it noisily interfere with our morals. It's a shame in my opinion that only one brutal act of the war (the holocaust) is taught, it seems to give the impression that it was an isolated freak occurance, but sadly, even to this day such occurances are not so rare.
Unit 731 was horrific and nightmarish. It was on an equally morally deprived footing, if not worse, than the hollocaust. Read up on the rape of Nanking
if you want to read more about what the Japanese were capable of during WW2 as well. What strikes me is the imagination some of the Japanese displayed. I despair that people with such imaginations and intelligence focused their energies on the systematic liquidation of human beings.
The Japanese method is a reasonably good argument for attempting to end the war quickly with atomic weapons. During WW2 my grand dad was stationed as an infantryman in India, and him and his friends were petrified of being sent into action in Japan. Stories of ferocity of the battles leaked back to the common solider, and scared them to death. No one wanted to go there.
Arguably also, (and I hope this splinters into a discussion on the topic), the estimated deaths of a land invasion would be far far greater than the bombs. On some of the small islands the Allies invaded, when they approached small villages mothers would jump off cliffs holding their babies because they were convinced by Japanese propaganda that the Western people (who most of them had never ever seen) were there to kill, torture and rape them all. The 'fight to the very end' mentality is a very good deterant, but when it is obvious they are going to lose, it's a very good way to waste a lot of life.
Flags of Our fathers the book, is a superb books which captures the ferocious nature of Japanese warfare very well, a lot better than the films. It contains graphic details that the films couldn't really get near. The book is fascinating, as it's central subject is that famous photograph. A stunning photograph, that seems to stir a sense of patriotism in me and romanticism, symbolising the struggle and sacrifice for an unarguable good quintessentially, where the cause far outweighs the needs of individuals.
The photo was taken on Iwo Jima, I think deaths per square km wise this was the most deadly place you could be in any stage of the war as a combat troop. A disturbing and tragic battle that lasted around 6 weeks over an area about 8 square miles big. 24,000 people died on those 8 square miles. That's 3,000 bodies per square mile. That's 70 deaths per square mile every single day of the battles. Of the roughly ~18,000 Japenese deaths, only around 200 were taken prisoner. That's how unforgiving Iwo Jima was.
It seemed in WW2 the further East you went, the more horrific and unforgiving the battles were. At least in Western Europe, a certain degree of ethics was for the most part displayed by fighting troops.
For a German troop in France, a severe punishment was to be sent to the Eastern front. As well as being an effective punishment, it actually backfired a little, as seasoned Eastern Front German troops who were reinforced with punishment soldiers wondered why they were there at all.
The Russian German war was a terrible event. The clash between differences in political ideals became more polarised. The modern age of media unleashed it's power as well in the form of efficient and mass propaganda. It fuelled hatred and racism. This in turn caused the battles to be particularly despicable.
'In Deadly Combat' and 'Sniper on the Eastern Front' describe some harrowing events in visceral detail. And how many more of these events happened, to real people that will never be known? Fields turned into meat grinders with mud boiling from non stop artillery, and people being forced to run into it. A German Flamethrower tank that found a pocket of a few hundred Russians in a hole in the steppes and charged in with them, the cries of hundreds of men burning to death and the tracks churning flesh. Faces grinning in agony before their bodies burst as tanks rolled over them. WW2 was the beginning of the modern age of mechanised warfare, and all the horror that brought along with it.