If we had to choose a definitive example of this to the Present Day Real Life, it would probably be World War II. While lots of wars have happened in the meantime, it was the WW2 that had in one way or another shaped the modern world and affected its inhabitants for generations to come. And, of course, it will remain off-screen until a Time Machine is invented. It has also affected a wide swathe of fiction since then; even Harry Potter mentions it.
This has some interesting consequences even in fiction that doesn't reference WW2 in any way: whenever a post-War author introduces an off-screen war Exactly Exty Years Ago, it will often take place about the same time ago in-story as the WW2 did in Real Life at the moment of writing (give or take a decade).
Arguably, this trope is particularly prevalent in Japan, given the country's complicated and somewhat contradictory approach to the second world war, and to warfare generally. There's a whole raft of cultural things that contribute to this, and most of them aren't in themselves unique to Japan, but the combination of all of them plus the political climate of the region cause a willful ignoring of WWII by general consensus in a way that doesn't really happen anywhere else. While it's not exactly taboo to discuss the second world war, there's a general sense that it's 'all in the past' and, while knowing about WWII is important for understanding the current state of affairs, there's no need to dwell on the country's past failures (other states nearby don't see it that way at all, of course). This social trend tends to carry over into culture, perhaps most notably in the general scarcity of military stories that aren't either pre-modern or science fiction. The point, though, is not that there's few modern-era war stories, more that the attitude of mentioning earlier wars as underlying causes without examining them too closely has found its way into Japanese fiction generally.
