1

Cut off from vital supplies by the Scream

2

Internal strife that led to city-ruining sabotage

3

Slaughter by some invading power that then left

4

Religious or ideological mania killed everyone here

5

Random cosmic mischance, radiation, or solar flares

6

Forced relocation by a great and indifferent power

7

Nanite malfunction or other tech failure

8

Exterminated by out-of-control machines or AIs