I'd go full alien influence on humanity here and make them the reason the Roman Empire was so successful. All those great Roman structures, their economy, and military prowess are only possible because of alien influences.
In the past, or the future?
I'm imagining angsty teenagers dressed in black trashing an H&M superstore. In Rome.
There’s a John Waters movie somewhere in there.Absolutely in the future!!! lol!
The man responsible for rhe children's crusade
I remember reading the short-story version in Analog and liking it - in part because it lacked a 1340s storyline. It was just the future timeline where "Aliens crash-landed in 1340s Germany, died and were buried there, and we're just now (re)discovering this." When the expanded novelized version came out, I knew I wouldn't like it, didn't want my appreciation of the short story ruined, and so didn't buy and read it.For. Wildly different sort of story, there’s Eifelheim, by Michael Flynn. It has two storylines. In the modern day, an interdisciplinary research group pokes at the mystery of how one particular German town got isolated just before the Black Death. The other takes place in the 1340s, as we see what happened to that town when an alien spaceship materialized there.
Fair warning: it’s a tragedy. And not one with cartoon stock villains. The audiobook excels, with the reader keeping everything the aliens say to humans absolutely flat, since their translation decides don’t do any emotional shading. Hearing them they ways really helps the listener grasp why some crucial misunderstandings happen.