One thing you can state with utter certainty. The Caretaker protocol is a testament to the art and genius of the ColonyCorp engineers. The robotic hivemind, designed to take care of the colonists in every possible event to occur, produced an impeccably neat and organized mass graveyard with what resources it had at its disposal.
It has been a long and brutal war. The Hrangaars are bound to lose. They are technologically inferior, and their diplomatic skill stops at asking their potential allies whether they wish to be destroyed or enslaved. Heck, they are even stupider than us, as was biologically proven. But in their objective idiocy lies their strength. They have the numbers, and they refuse to give up. We had to annihilate dozen of their slave races before we managed to finally defeat the first world of their pathetic empire. Eventually, we realized we could not afford to play by our rules anymore. Every invasion was paid by a staggering amount of dead humans.
So, two years ago, we tested the first biological warfare cloneship, Ark. A leviathan of a spaceship, filled to the brim with biological samples of the most virulent and deadly diseases, and the most lethal apex predators we could collect. A single strike from such vessel was supposed to render a whole world dead, in a very literal sense of the word. The test was done on a nameless Hrangaar world. After the escort fleep blew the orbital defenses up, the Hrangaars started to fortify the major locations on the planet below. It must have been quite a surprise, when instead of a myriad of drop pods and planetary assault ships, a single, ominously large ship dropped from the FTL just above the planet's capital, and parked in low orbit, where it was easily seen to the naked eye from the surface. A single bomb was dropped from this vessel, guided through the anti aircraft fire by the powerful computers aboard. It made a successful planetfall, and released a nameless organism, a virus merged from a dozen blackest biological nightmares the humanity has encountered between the stars.
Two days later, the virus was the only living organism on the planet. Five days later, it died off, leaving behind a dead husk of a world.
Or so we thought. Somehow, one of those mongrels got away with a sample. I imagine him bleeding from every orifice, eyes turned to black, dripping sludge as his ship landed on the Hrangaar world where he made his escape. He made sure to inform the personnel at the cosmodrome to not open his ship, that he was carrying a great weapon, stolen from the enemy. They were too dumb to adapt it, learn from it, but perhaps they figured out that this time, they knew something we did not.
Week ago, they returned our weapon to us.
Today, the fifth clone ship is being christened, the Erebus. Tommorow, the cloneship fleet will set sail. Their worlds will be wiped clean of life, and this war will be over.