I'm looking for an old science fiction book.
In the book, the Earth was destroyed by an alien race, and all of mankind was destroyed except for a group of people who were off earth at the time.
They spent hundreds of years rebuilding themselves and making themselves more powerful. After centuries, they went out into the galaxy to take on this alien race, only to be almost destroyed again.
This happened a couple times, until mankind had reinvented themselves as almost invincible people. At that time, they again went out and defeated this race.
I seem to remember that the name of the book was Space Lords, or Lords of Space, or Space Kings, but I could be wrong. If anyone remembers this book, I would love to know the title so I can see about buying a copy. Thanks!