The Baldic League

Savages on a hundred planets got spaceships and nuclear weapons while remaining savages. (As the Technic History developed, both its author and its readers came to understand that the savages were armed by unscrupulous traders within the Polesotechnic League.) There are engineers who sacrifice to their converters and generals who depend on astrology so trained human beings are valuable slaves.

Some kings formed the Baldic League which defeated Solar forces because the Commonwealth had been weakened by civil wars. (We know that its first internal conflict was the Babur War.) Some human extrasolar colonists have reverted to barbarism and joined the Baldics against Earth. After the first sack of Terra, the League split because its founders were dead and their sons fought over the inheritance. One League faction conquers the outer Solar System and raids the inner planets for slaves while the Commonwealth government hides or no longer exists.

Manuel Argos, a slave on Gorzun, knows enough practical engineering to get a master in whose factories he learns more. His master sells him to the captain of a slaver ship where Argos easily becomes the de facto engineer, systematically sabotaging the engines until he can identify fellow slaves with technical training who will help him to take control of the ship. The days of the already divided Baldic League are numbered.