War crimes are what the winning side accuses the losing side of doing.
No one should have the slightest doubt that if Japan had won WWII, then Hiroshima and Nagasaki would have been considered war crimes. The Japanese-American relocation camps would have been considered war crimes.
I do not accept the designation of "war crime". Throughout all of history people engaged in war have done bad things. That's just the way it is.
And eventually it comes full circle, the used-to-be winners lose big enough to be in the dock, accused and guilty of violating the same laws they made up to legitimize their taking of heads when victorious.
The moral: always win big or be dead before you lose big.