I'm not sure whether it was the translator messing up or the author trying to disguise his intentions, but I'm certain the author meant to refer to WW2. Given that the author got in trouble for going on racist rants against Chinese and Korean people online, I think it's safe to say he's a bit hung up on that war.You're thinking of WW2 not WW1.
On the other hand, the uniforms that the artist drew in this chapter are clearly WW2 uniforms so I'm kind of confused.