Who was the most brutal army in World War 2?

Answer 1

If you measure brutality by the treatment of captured soldiers (POWs) and of civilians in occupied areas, then you have pretty much a tie between the Imperial Japanese Army and the Waffen SS.

The IJA has a long history of murder, rape, and maltreatment of captives, both civilian and military throughout WW2. Much of this came from two sources: the Japanese soldier was taught to revere death in the service of the Emperor as the supreme duty, and thus surrender was beneath contempt, and those who surrendered were not worthy humans (and, thus, could be treated as such); the second source was the historical view that Japan was the Land of the Gods, and that as such, the Japanese people were specially blessed, and that all other peoples were lesser beings. In addition, the IJA practiced draconian discipline upon the ordinary soldier, so much so that orders were unquestionably obeyed, on pain of death.

A similar case of group psychosis was found in the Waffen SS, who believed in the racial purity of the Germanic Aryan race. Brainwashed into believing that such a race existed, and that it was the Ubermech (superhuman), and thus, had the moral duty to subjugate and enslave all lesser humanity, the Waffen SS went about a ruthless campaign to rid the world of such lower beings (usually by immediately killing them, though sometimes torturing them first). Such killings were a service to humanity, and thus, routinely encouraged (if not actively planned, which many of them were).

It's hard to say who was worse. The IJA "wins" on total bodycount, and was a much more indiscriminate killer of the innocent. The Waffen SS "wins" on efficiency - there are few known organizations more efficient at killing their intended targets than the SS. The fact that in both cases, the majority of their victims were civilians only points out how awful both were.

Note that all armies in WW2 were brutal in some form or the other; however, the IJN and Waffen SS stand apart in their abject, systematic brutality.