Staines [they/them]
The difference between the empire in Star Wars and the Imperium is that the Imperium is essentially inescapable.
It has endured for 10,000 years, it has a million worlds. Non-human intelligence is mistrusted at absolute best. Separatism is not tolerated, Alderon was just Tuesday morning, and probably literally a quadrillion people thought they deserved it anyway. Communications and travel can take hundreds of years depending on the conditions, so a response fleet might not even arrive in your lifetime, or your children’s lifetime, but it will come, and even a low estimate of the Imperiums levy would mean they command around a trillion soldiers.
Basically the Imperium of Man is a suffocating, unstoppable, grinding hate machine.
It is human society twisted into eternal, nightmarish, inescapable horror.