Approximately a millennium elapsed between the breakup of the Martian colony government and the emergence of the Dark Republic. After the second civil war in the early 4100's, the Martian population stabilized and began to grow. However, although there were periods of relative abundance, the expansion of the industrial base was never able to outpace population growth for very long, as intercolonial warfare or the periodic reemergence of TYRANT servant-cults among the psychologically vulnerable would inevitably destroy whatever progress had been made.
Martian society of the fifth millennium is typically described as guild-feudalist. Skilled occupations split into hereditary guilds, which jealously guarded their prerogatives and operated the industrial apparatus. Ownership of that apparatus, and control of the military, was held by a hereditary, hierarchical noble class. The balance of the populace, lacking skills or property, lived in destitution, serving as a reservoir of manpower for the guilds and the military to draw on as needed. The desire to maintain the privileges of the elite class led to further mal-distribution of resources, such as refusal to train additional workers in critical skills since it might mean dilution of guild control. Although the details varied widely from place to place and from time to time, the broad outlines were remarkably consistent over the centuries.
Martian politics was defined by group separatism, with the various colonies wasting their energies struggling amongst for resources and dominance. Alliances between colonies were inevitably temporary and fractured the moment it became politically expedient. Although the governments formally expressed a desire to retake Earth from the Enemy, they took no action to achieve this.
Political Boundaries on Mars in 5,000 AD
(Image Credit: http://en.wikipedia.org/wiki/Geography_of_Mars)
Martian Technological Regression Under Guild-Feudalism
Although little of humanity's scientific knowledge was actually lost, much of it was sequestered in closed archives, and much else could not be implemented due to lack of materials or infrastructure. In particular, the crystal matrix computers and batteries used during the Second Golden Age could not be replicated by Martian industry, since necessary elements were not available on Mars; Martian engineers reverted to using silicon-based electronics and lithium-metal batteries that had been obsolete for over a millennium.
Biologically, the Martian populace benefited from substantial genetic modifications. These modifications had been developed during the Second Golden Age to support exploration of the Martian surface, using retroviral inoculation: thick, rough, orange skin covered with a thin layer of orange, brown, black, or gray fur, except around the face and extremities; large, infrared-sensitive eyes with a transparant coating to keep out dust; increased blood oxygen capacity; and a thin layer of blubber around the crucial organs. These enhancements allowed Martian colonists to survive for up to thirty minutes without protection outside, and indefinitely with only a parka and airmask.
The only widely-used form of nuerological engineering was the trimind. Triminds were a predecessor technology to modern polyminds, produced by genetic engineering of the zygote rather than by post-birth modification. A trimind resembled a short, squat, fat Martian human with a small head. They had three brains, mounted in their torsos rather than their skulls, linked by a large nervous column. Each brain had access to the same sensory information as the others, and the nervous activity of one was relayed immediately to the others. Essentially, a trimind was a single person, who could maintain three separate tracks of thoughts simultaneously. Creating and maintaining them required extensive medical support, and they typically lived for only 40-50 years, so they were not common. However, both guilds and nobility found them extremely useful, particularly in planning and operating the Martian city economies.
The Martian colonies relied primarily on nuclear fission for energy. After the second civil war, there were periodic attempts to revive space travel, usually for military advantage, but the poor industrial base and sabotage by competing factions meant few of these efforts were successful. Military technology was primarily chemical energy weapons, including projectiles and missiles, and low-power ultraviolet lasers, primarily for defense. The ultimate weapon for the Martian colonies was the fission/fusion bomb, typically delivered by short-range missile.