Let's see... I ought to come up with something that I don't see mentioned very often...
How about "The Damned", a trilogy by Alan Dean Foster?
A scout ship from a group of allied species called The Weave discovers Earth, and are shocked by what they find. Most species known to them are psychologically incapable of acting violently; at least one gets very sick even contemplating the idea. By their standards, even the most mild-mannered of humans are incredibly dangerous. This turns out to be a very useful discovery, as they are currently in the middle of an interestellar war... But what happens when the war is over?
How about "The Damned", a trilogy by Alan Dean Foster?
A scout ship from a group of allied species called The Weave discovers Earth, and are shocked by what they find. Most species known to them are psychologically incapable of acting violently; at least one gets very sick even contemplating the idea. By their standards, even the most mild-mannered of humans are incredibly dangerous. This turns out to be a very useful discovery, as they are currently in the middle of an interestellar war... But what happens when the war is over?