A Witch in Mongolia

I've heard good things about Vineland Saga not shying away from its depiction of generational war. Somebody told me it's one of those where everyone kind of sucks but it will give you context to why the violence is happening. Been on my watchlist but I haven't gotten to it yet (I'm dragging my feet because I've come to hate vikings in media)

Really depends on the era.

Gate is pretty realistic for the whole modern warfare vs ancient roman warfare.

Grave of the Fireflies is a classic.

The Saga of Tanya the Evil does a surprisingly good job of it, considering it's an isekai about flying mages.

Much of it is not-Germany fighting not-Russia while not-Italy are acting as neutral peace facilitators while not-UK are harrying the western flank, and they're worried about the not-US getting involved and screwing up the balance of power. Lots of politics and strategy mixed in with some good action.

The Cockpit might be of interest (if you can find it—I'm not sure there's any current streaming license). Zipang, too. There are probably others I'm forgetting about.

I’ll argue the first Gundam

I think "In This Corner of the World" does a pretty good job.