In 4056 BBY when new, smaller trade routes moved from Taris, rendering the planet unnecessary and without the support of the Republic, the planet began to fall into ruin and despair. The great city of Taris covered more than half the planet's surface rendering farming virtually impossible; kelp harvests and the sea creatures were the only food source.
It was at this time that a self-sufficient colony beneath the Undercity was discovered, which was the only part of Taris that was not urbanized, and in which farming was possible.
Abandoned by the Republic, the Tarisian industrialists began to use the power source of their wish, which produced a form of toxic waste. The pollution levels rose enough to poison and kill most of the oceanic fauna and flora, and the planet was swept with famine. The Tarisian elite hoarded the remaining food and wealth for themselves — far more than they needed — while the poor were left to starve and die.
The Tarisian poor, disgusted at what the rich had done, rebelled against the rich. The full extent of the war was unknown, although millions of civilians died during the conflict, and many large city sectors were destroyed or abandoned.
When the uprising was ultimately crushed, thousands of rebels were imprisoned. The jails soon became overcrowded, however, so the excess rebels were instead banished to the Undercity, unable to return to the surface under penalty of death. These exiled prisoners formed a group of people in the Undercity known as the Outcasts.
All hope was lost to the defeated rebels, save for one; the prospect of the self sufficient colony in which farming was possible, which they dubbed the Promised Land. Gendar's ancestor led the Outcasts to built the Outcast village in which they might survive.
Due to what they deemed as the success of the banishment process, the officials in the Upper City decided to render all of their prisons in the Upper City obsolete, preferring instead to permanently banish any and all criminals in the Upper and Middle City to the Undercity. Here, walking the original surface of the planet that never saw the sun due to the shadows of Taris' massive skyscrapers, they endured a lifetime of horror marked by starvation, rakghoul attacks, and rakghoul infections. Even their descendants were forced to suffer the punishment of their parents, even though they themselves had done no crime.