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human
[Warhammer 40k] How does the Imperium integrate new worlds?

Say the universe decides to throw the Imperium a bone and they rediscover a system with a habitable human-occupied world and the local population doesn't or can't fight the occupation. How would they set about establishing planetary governors, local arbites, ministorum tithes, development of necessary stellar infrastructure (Starports and the like), etc?

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(Disclaimer: I'm mostly asking from a pre-fall of Cadia perspective, as I kinda dropped off from 40k around the time The Gathering Storm was released and I haven't kept up with much of the lore past that.)
gpt
>How would they set about establishing planetary governors, local arbites, ministorum tithes

They don't need or care to. As long as the system's religious beliefs aren't outright heretical, it's cool with the inquisition. Just add a little footnote at the end of their sacred texts that say "oh and by the way every time The Great Ancestor Spirit is mentioned, it actually means The God-Emperor of Mankind", and bam, their religion is within the acceptable variance of the Imperial Cult. So that's religion sorted.

For governance, they can govern themselves however they want. Republics are fine, tribal systems are fine, feudal systems are fine, corporate systems are fine, as long as the Imperium is recognized as the final authority above whatever is at the top of the chain of command on that planet, it's all good.

Same thing for the Tithe. If they have a reasonable amount of psychers, regiments, resources and manufactured product to give to the Imperial ships every time they come into the system, they'll be fine. 

Reorganizing the whole system's political, religious and administrative system is only going to fuck with the industrial output of the system, and nobody wants that. Don't worship the ruinous powers, humor Imperial Administrators whenever one shows up, and pay the Tithe every time a starship comes, and nobody will ask for anything more.