Just a quick point:
There is no reason (other than military) that the Aslan couldn't use nukes
to clear a planet of unwanted inhabitants. A nuclear damper (carried by
many of the Aslan warships) can clean a radioactive area quite quickly.
Sure the bombs would knock down all the buildings, but the Aslan don't
strike me as the types who would particularly care about that.
And if they did want to take an area intact, there are always neutron bombs.
Scott Kellogg
"Look out! The Aslan Admiral's been smoking catnip!"