In military jargon a Theater is an area or place in which important military events occur or are progressing.
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WWII by it very nature has a variety of tones (bravado, Gritty, and extremely dark) and crossovers genres (GURPS Horror, Classic: Black Ops, GURPS Thaumatology, and Transhuman Space to mention a few). There is even a "Technomancer 1942" (Merlin-3).