The Japanese have been downplaying the Nanking atrocities since the siege of the city began; Japanese journalists following the Imperial army wrote dispatches about the valorous deeds of their soldiers. Japanese textbooks were heavily censored,leading to a lawsuit by Japanese professor that took 32 years to resolve.
So, grudgingly, the Japanese have begun to acknowledge their sordid past.
Meanwhile, here in the US we've also had a change in outlook about our past.
The massacres are rarely mentioned at any length in most modern books I read recounting the origins of the Second World War,or by my students, when they enumerate the causes of American entry into the Second World War, but rising American determination to stop Japanese aggression in Chine spiked sharply when news of the massacres reached the United States. It is more common than it used to be to hear that by 1941 the U.S. had backed Japan into a corner, leaving Japan no choice but humiliation or war, and it’s much less common than it used to be to hear about what moved American opinion to push Japan so hard. Japanese rightists explain government-backed Chinese interest in the Rape of Nanking as a cynical excuse for mobilizing nationalist sentiment. This may be true, but Japanese inability to face the fairly recent past is at least as remarkable as widespread Chinese interest in a crime of such magnitude. What is more remarkable yet is that although the numbers murdered in Nanking may be the equivalent of three or four Hiroshima bombings, no phrasemakers describe the horrors of the twentieth century as those of “the age of Auschwitz and Nanking.” “Auschwitz and Hiroshima,” however, has become a familiar yoking of crimes. The politics of historical memory has in recent decades been a popular topic in my profession. Oddly enough, the people who profess the greatest interest in it seem likeliest to have the most imprecise and wispy memories of the Rape of Nanking.
... it is common to hear that by 1941 the U.S. had backed Japan into a corner leaving Japan no choice but humiliation or war ...