War rape hentai?
I find it interesting to think about how mass rape and plundering of cities would have been a common occurrence for thousands of years with all the constant wars in history. It is quite an exciting thing to imagine yet for some reason it is hard to find any such hentai.
There are two titles that immediately come to mind.
"Black Shell"/"Dark Shell" features groups of women being led by a military force, being raped and murdered along the way.
"Adventure Kid" is a classic anime where the MC and GF are magically transported to WWII Japan - more rape and death with soldiers with a unique scene with American nurses that is really a aquired taste.