Earth was out in space and a species almost eradicated us, we breed super humans and fight back
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This is the premise...

Earth was starting to settle and explore far space.
A species finds us and in no time almost eradicates us except for some far-flung pockets of survivors. The species takes over Earth and every place we have been.
Over millennia we breed a super species of earthlings (star kings?) who become so powerful they fight with the aliens and destroy them all.
We then find out all this was planned by a far superior species who was fighting a war that has been going on for many thousands of years and arranged all this to develop a species of warriors to help them fight their war on the far side of the universe.

I thought the first chapter started with "the star kings are gone" and then went into the story above.