In 40k lore the Imperium, during its expansion, encountered a highly advanced society where everyone's needs were being met, everyone was equal, and there was no poverty, stratification, or anything else that creates discord. As a result this society was basically untouched by the Chaos Gods.
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Also "no stratification" is a stretch for a society with a literal caste system.
It would be a human populated world that worked with aliens in a society that worked to meet everybodies needs with low changes of a chaos incursion.
Now if there is some other totally unrelated planet sure.
also that they *worked with* aliens; implying they themselves were not, when the T'au very much are
If i can ask who you were talking about?
I didn't name them before because I couldn't remember what they were called
By creating a society that was better for everyone they had effectively neutralized Chaos entirely.
Possibly the only society in the galaxy that knew how to defeat Chaos; destroyed by fascists who thought they knew better.
One of the many examples that the 40k setting is satire that mocks fascism and not an endorsement of fascism, as chuds seem to so wrongly think.
Then they introduced the brainwashing/mind control stuff and honestly kinda ruined it.