The Alliance Trilogy Series by Michael Wallace

Captain Jess Tolvern of HMS Blackbeard is leading a Royal Navy expedition across long-dormant space lanes toward Old Earth when an alien fleet ambushes her battle cruiser. The aliens are Adjudicators, an ancient race whose ethos is to judge other species and reduce their survivors to a stone age existence. Tolvern sends a desperate message back to headquarters and retreats with her damaged ship to friendly systems... moreCaptain Jess Tolvern of HMS Blackbeard is leading a Royal Navy expedition across long-dormant space lanes toward Old Earth when an alien fleet ambushes her battle cruiser. The aliens are Adjudicators, an ancient race whose ethos is to judge other species and reduce their survivors to a stone age existence. Tolvern sends a desperate message back to headquarters and retreats with her damaged ship to friendly systems. By the time she returns, the aliens have already invaded Alliance territory with a powerful fleet of star fortresses and accompanying dragoon ships, trapping and laying siege to the allied fleet. While repairing her ship, Tolvern cobbles together a squadron of damaged allied warships, former raiders, and the local survivors of an Adjudicator attack to drive off the alien fleet. less

After fending off the Adjudicator attack, the Alliance learns that the enemy is preparing a final, exterminating push against the human systems and their allies, the Hroom Empire. To buy time while building their forces, the allies send Captain Jess Tolvern and her sometimes rival, the former pirate Catarina Vargus, in command of a fleet to raid and reconnoiter the aliens’ own home worlds... moreAfter fending off the Adjudicator attack, the Alliance learns that the enemy is preparing a final, exterminating push against the human systems and their allies, the Hroom Empire. To buy time while building their forces, the allies send Captain Jess Tolvern and her sometimes rival, the former pirate Catarina Vargus, in command of a fleet to raid and reconnoiter the aliens’ own home worlds. They cross the inner frontier into systems torn by novas and black holes to find the aliens, who have hidden themselves in a previously undiscovered system, where they are awakening an ancient machine with the capability of devouring entire starships. less

An apparent naval victory turns to chaos when the Adjudicators awaken an ancient star leviathan and send it against the allied fleet. Falling back to friendly territory ahead of this terrifying weapon, Jess Tolvern and the allied command muster the combined forces of the Alliance planets to finally defeat the Adjudicators and push across the inner frontier to reestablish contact with the remaining civilizations of Old Earth.