GoodReads Summary: Humans expanded into space... only to find a universe populated with multiple alien species bent on their destruction. Thus was the Colonial Union formed, to help protect us from a hostile universe. The Colonial Union used the Earth and its excess population for colonists and soldiers. It was a good arrangement... for the Colonial Union. Then the Earth said: no more.
While all the other books in the series are more about "fight" and "tactics", this is way more political.
After all the events in the series, the story finally reached a point where a cold war is present and the "action" is more about talk and creating pacts than exploding stuff. Which, to be honest, felt like the natural way the story should go.
If you like the explosions and stuff, you may feel a bit down by this, but you have to give a change for the exploration of all other aspects of the universe created.