Reclamation (The Art of War Trilogy)

Centuries in the future, humankind, an interstellar hegemony operating under the umbrella of the UN, exists alongside five other advanced alien races. Together they form "Tier Three", bound by a diplomatic and trade accord by which little is certain except distrust and conflict. When the kaygryn launch a suicidal assault against an Ascendancy crusade fleet, the fragile imperial compact is thrown into disarray. The Ascendancy is quick to retaliate by massacring the kaygryn, and with a human colony in the midst of the crisis, the UN launches a series of heavy-handed military interventions which succeed only in embroiling it in a deadly alien war. Four UN officials - a petulant strike commander, an ill-informed mecha pilot, a decapitated intelligence agent and an elite, narcissistic diplomat - unwittingly share reservations about the provenance of the conflict. And when the Ascendancy's crusade fleets - vast naval armadas which have been mysteriously pouring into the next galaxy for centuries - begin to slow down, it soon becomes clear that the very survival of the human race is at stake...