Space marines have ships that can disperse a planets atmosphere due to its size...i love both universes but super star destroyer is a toy compared to these ships. Chaos, @ the omment that chaos will just fight each other, no do you know anything that chaos does? They have daemons and infinite amounts of devotees at their hands ready to destroy at their masters wills. Not to mention the gods. Throw all the other 40k races in the star wars universe and you got total chaos. 40K would be the winner but then the races would resort to fighting each other again.
Again you asume 40k is going to focus on the star wars armies.
Between the imperial of man, chaos, tyranids, eldar, necro's and who know's what else killing eatchother.
It is quiet possibol for star wars to survive.
And if you read correctly i never said they could win militery speaking(second line)
The star wars universe much rely on staying below the threat radar until they can level the field.