What the 'Space War' is might be an interesting story. We seem to have this little bubble dimension which seems to be designed for Sensei in which we have this weird ass war that makes absolutely no sense whatsoever and no one questions it. This seems to be because they are all controlled in some way. (At one point, Makoto realises that having two annual beach trips in one year obviously doesn't make any sense but then gets forcibly reset to not have ever thought it, no one else even seems to consider this even though it should be obvious) What the Space War is, is an intentionally dumb excuse for why no other guys are around to be competition for Sensei as he parades around and grooms a bunch of girls in a world made for him.