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Is the crimes of Japan greater than those of Germany, or the USSR?

By what standard would you suggest we use for measuring this? I think that as historians we can discuss the morality (or lack thereof) of various actions relative to various standards of conduct, but declaring a "winner" in what some historians call "the Genocide Olympics" would be a difficult--and quite possibly futile--task.

What were some of the questionable action's taken by the western allies?

One could examine the bombing campaigns of the various Allies, as well as the practice of unrestricted submarine warfare. The question again would be what standard would you use? International law on these issues wasn't a cut and dried issue (there are questions about whom the law applies to and what the law prohibits exactly), and applying any particular culture's sense of morality to another culture's is problematic.