Metal swarm - Kevin J. Anderson

The alien hydrogues have been defeated, driven back into the cores of their gas-giant planets by an alliance of the Earth Defence Forces, the ancient Ildiran Empire, the gypsy-like Roamer clans and fantasic water elemental beings as well as gigantic living 'treeships'. But as the various factions try to pick up the pieces and recover, the deep-seated wounds may be fatal.
The Hansa's brutal Chairman Basil Wenceslas struggles to crush any resistance even as King Peter breaks away to form his own new Confederation among the green priests on Theroc, the Roamer clans and an ever-growing number of breakaway colonies who have declared their independence. Like jackals smelling wounded prey, swarms of ancient black robots built by the lost insectoid Klikiss race continue their depredations on helpless worlds with stolen and heavily armed Earth battleships. A race of capricious and terrifying fiery elementals, the faeros, has joined with an Ildiran madman to declare war against all life. And the original, voracious Klikiss race - long thought to be extinct - have returned, intent on conquering their former worlds and willing to annihilate anyone who happens to be in the way.