Empires at War: Book 1 — Doug Dandridge

Humanity's worst nightmare has again come out of the Dark. Can a human race in turmoil survive?
When the human race faces extermination at the hands of an expanding species the last survivors travel a thousand years to reestablish the race ten thousands light years away. It is now a thousand years after the birth of the New Terran Empire. The race has aggressively expanded during that time, with a fleet that has never lost a war against an alien species. But the signs are there, the old enemy is back, and the Fleet will face its greatest challenge in a foe fifty times their size.
Science fiction in the tradition of Anderson and Weber, where the physics of normal and hyperspace dictate the strategy and tactics. Enormous fleets battle across the immensity of space with advanced technologies. Can the proud human Fleet hold off the tide of an advancing enemy, rallying allies and deploying new tech? Or will the conquerors achieve what they could not two thousand years before, and end the existence of the upstarts.