Apocalypse Meow Its a fairly serious manga about Vietnam, but all of the characters are cats and rabbits. I haven't read it all the way thorugh so I do not know why they are all cats and rabbits, but they are.
Well, you're not going to find any manga about modern war (such as the fights in East-Asia and stuff), so the closest thing would probably be realistic science-fiction war manga, like;
Eden
Akira
Appleseed
Mother Sarah
If you don't mind reading older war manga, then I suggest;'
Zipang (WWII)
Adolf (WWII)
Who Fighter with Heart of Darkness (Vietnam)
Apocalypse Meow (Vietnam)
Barefoot Gen (post-WWII)
Yûnagi no machi; Sakura no kuni (post-WWII)
Good-bye (TATSUMI Yoshihiro) (post-WWII)
[m]Apollo's Song[/m] (WWII)