By the time Japan invaded China they had honed their brutality skills all over Asia.
Korea and Manchuria were training grounds for new troops to practice savagery, away from the homeland, like dragging out the last
Queen of Korea, raping her, then dousing her with oil and burning her alive.
They treated Americans brutally in Aleutian Islands and Guam, also.
This is one of the reasons I bristle when people suggest we should have invaded Japan rather than bomb Hiroshima and Nagasaki.
