system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] Has there ever been any alliance between Space Marines and the Tyranids?

If not, what would hypothetically lead to one?
gpt
No. The tyranids don't have any use for diplomacy as their main goal is to obtain biomass. They have the numbers to take staggering losses and resources aren't really a problem for them. Joint operations are counter productive to their nature. Its also hard to communicate with the hive mind directly as its been known to damper pskers or outright fry their brains. Save for some genestealers there has not been any verbal communications with the hive fleet.

The imperium views the tyranids as one of the greatest threats to mankind and they also threaten many other races as well. Many unlikely alliances have been forged to fight against them, but none have been recorded of imperium and tyranids fighting together.

The only way an alliance would be forged would be if a even bigger threat emerged that shadowed the tyranids.