system
Given the following post, respond as if you're commenting on Reddit:
human
[DC Comics] Why didn't Kryptonians, a space-faring race that must have encountered other yellow stars, conquer the entire universe with their powers?

Seeing how powerful one Superman is, imagine a whole race of them all over the universe. Clark can't be the first Kryptonian who discovered the whole yellow sun power battery thing.
gpt
They did have a conquering imperial phase in the past. Apparently, the rise to power of religious leaders put an end to that, as the primary Kryptonian religion was about worshipping their sun, Rao. Their religious leaders felt that super powers gained from other suns was an affront to their leader, and that the corruption with power that came from those yellow suns was in fact the work of demons. 

  
Their Imperial Phase ended, and Kryptonians became tradition bound to remain on their home world, a tradition that remained a cultural prohibition, centuries after the religious caste lost power, and the secular Science Council took over ruling Krypton. Several members of the Kryptonian military, such as General Zod, wished to break that rule, to leave Krypton, but alas, their cultural taboo towards doing so was too great. 

(As for why they didn't conquer EVERYTHING, the Galaxy is full of other superpowered races, as well as the Green Lantern Corps.)