system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40K] A human civilization stronger than the Imperium appears in the Galaxy. What would the Imperium do?

Let's say that, during the Dark Age of Technology, a bunch of humans ended up VERY far away from the Imperium for some random Warp accident, and they not only managed to survive but also thrive and become much stronger, bigger and more technologically advanced than the Imperium ever was.   
Let's also say that Chaos is not really a problem for them: maybe they developed some anti-chaos field technology, or maybe they have an unusually high number of Blanks (1 in 10 people), or both.   


Anyway, these guys one day come metaphorically knocking at the Imperium's door. They are not hostile against the Imperium, and in fact may even be open to an alliance and leave the Imperium alone. They are not, however, interested in joining the Imperium nor the Imperial Creed, and maybe, while wary against aliens, are not complete xenophobes like the Imperials and are open to trade with Eldars and Tau. 

&#x200B;

They are also so powerful that this "trusting" attitude can't bite them in the back too hard, cause if they wish they could easily annihilate whatever species they fight against (to the point that Orks and Tyranids are more like an annoyance than a threat to them). And as discussed, they have reliable way to ward off chaos.   


What would the Imperium do? Would they want to be left alone, would they trade with those new guys, would they join them or would they attack them accusing them of being Heretics (despite the fact that they would lose)?
gpt
Of course they would attack them. They’re heretics, tech-heretics, mutants, and xeno-lovers. 

That they would lose doesn’t really mean anything (edit: or at least, wouldn’t really stop them). Suicidal devotion to their state and religion is nothing new to the Imperium.