Sure, but it took pretty much a rounding error amount of casualties, out of which approximately zero were regular civilians. Not sure why exactly it would be WW1 and not, well, the other one.
It's confirmed as WW2 later in the doujin, but admittedly not yet on this page.
Updated
it seems there's a war happening on the Outside.A war...!A real gruesome one, too.I wonder if that's it....That poor thing.I get the feeling she doesn't really want to remember.With all that going on, no one would notice if one person got spirited away.I heard from my fellow ferrymen, but...That's why we're suddenly flooded with phantoms.