Raiders of the Universes

Raiders of the Universes is a sci-fi novel by Donald Wandrei, published 1932 in the magazine Astounding Stories. In the 34th century, so called Raiders are wreaking havoc on entire planets around Sol; and Earth is no exception! The Raiders find out about intelligent life on Earth and 'kindly' decide not to eat it up like so many others...but what in turn might be worse?