The Raiders

Raiders were formed from the once mighty Terran military. They originated
with a Special Forces unit called "Black Ops". They were also subject to
covert bio-military experiments that killed many and left the survivors
sterile. The experiments proved an embarrassment to Civil Authority and
the survivors were denied help, let alone an admission of culpability or an
apology. They revolved, began raiding local worlds to take care of their
needs and bonded against all civilization in the process. A less than merry
band of outlaws, their raids were bloody, designed to exact revenge on the
rest of humanity, because they could not reproduce as a result of these
experiments, the Raiders stole young children to re-make as their own.
The Raiders are divides into many factions, known as clans. Sometimes,
there are battles between the clans and vendettas to be settled. But when
outsiders threaten, the clans unite....until now....

Raider Vehicles

These vehicles are sleeker than shuttles and are reminiscent of 20th century
fighter jets, except that the operate inside and outside of atmospheric
environments. They mount a variety of weapon turrets. They also have
aerodynamic surfaces (like wings or rudders) to make them more
maneuverable and thus capable of attack, in an atmosphere.
They are hybrid atmosphere/space vehicles with small nuclear rocket
engines and some wing surfaces.
The Raider vehicles descend from orbit, raid an outpost, then head back
with their booty. When in space, the Raider vehicles can join together to
form a huge body capable of interplanetary travel. These larger bodies are
thought of as raider "cities". The Raiders cannot obtain the thousands of
graviton coils necessary to equip this whole structure, instead, they slowly
rotate their "cities" to provide artificial gravity.