Districts: Phoenicia : War of Ascension :

 Phoenicia 3 colonisation and settlement history.

According to the Ark logs, which is the same protocol for all Arks sent forth from Earth.
The Colony Ships have a detachable nose section which carries Automated Reactive Constructors or Arks with ARCs. These separated from the craft once they came into the star system speeding ahead to the pre programmed landing zones to create the initial safe zones for the colonists. 

The Arks themselves would slow down and begin the safety checks, scans and gathering as much information about the new region as possible, which once complete would activate the wake up protocol for the inhabitants. Once more this is the same for all of these giant lifeboats. 

Phoenicia : War of Ascension.
Outside of the Central District no one actually knows what happens. It is called the War of Ascension but not a single shot was ever fired. The ruling house fell to illness, the other houses decided they wanted to run the colony. Everything within the Central District was locked down to deal with this and allow no outside interactions while discussions were held, votes were taken and so on. That was 200 years ago. The doors never reopened. 
Every Outlining District though still has to pass all its goods through the Central City, some for tithes and taxes some to be redirected off world? No one is really sure but if you don't meet your quota then the Automated Reactive Collectors come and get it, with extreme force. 
This in turn causes Districts to sneak into other Districts and "Borrow" items. 

The other possibility that happened inside the walls when the ruling house fell is simple the remaining houses just went to actual war, closed the doors and killed each other, the automated systems just carry on as they did before the City sealed. But no one is sure on either of these possibilities. 

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No one knows how to leave.Without the Central City being accessible, the expansion protocol has never been activated. No one living within the shields knows if the world outside is safe for human life, some have broken out but never returned.....

But this is never taken into account by the Gangs, they are just doing as their Districts ask of them and attempting to gain resources, tech and whatever they can from the other Districts. In order to pay the Central City and not have the ARCs come down on them. 

No one is looking past the walls to the world outside, or to the stars wondering where things are going or coming from. 

No one even remembers where they are from. This Colony has reached the point where it's past is lost. Everyone here was born here, and all of them are just trying to survive. 

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This is just one Colony. One. In a Universe of millions of worlds. Those initial Arks were sent out into the world as fast as possible and all of them have different engines, animation chambers, and shielding technology. So this is the first world that's about 300 cycles old.