This is a great sci-fi novella, packed with action, scheming, conflict, and twists. I loved the idea of a species Aggression index and how humans were underestimated. It's a thought provoking read that touches on humanities need for conflict, but having matured enough to be a peaceful species lying dormant in the background until a galactic threat emerges. I enjoyed the touches of humour and the range of characters. 
For a short book a lot happens but it's well paced, explores multiple POV, and contemplates themes of morality, genocide, alien invasion, political uprising, and alliances.
Would definitely recommend.