It's kinda like actual war. Everyone starts with some reason, and by the end of it they're like "wtf are we even doing?!". That's probably how the mangaka felt. In the end it was all pointless, like actual war.
Missing backgrounds is strange, but it's the end, and just focus on story and characters, like in all this manga.
A best one for me, very sad, displaying the useless of war, and the criminality of the governments.
