The point of the police in a society is that they have a near-monopoly on armed force, and therefore criminals can't hope to win by escalation. In a world where the US has by far the biggest military, it can to some extent arrogate to itself the role of a police force, which raises the issues you suggest.

WW2 is not this situation, and it's an anachronism to analyze it as such. Pearl Harbor was followed by a string of other US defeats. For a while, it looked like Japan would set up an empire from Alaska to Australia. You don't have the luxury of deciding to hold back in a situation where all your efforts might not be enough.