I have a underground culture that has been cut off from the surface for near on 200 years, and I am trying to understand what issues will I need to cover and am most likely to run into for there survival to continue.
A little back story, the world becomes so over populated that they begin to dig into the depths of the earth, over generations they get so deep that some people end up spending their entire lives digging underground to create a better life for their family, millions live in the depths of the earth now and the government has called everyone to the surface to solve the world's over population problem once and for all, those who left never returned, but those who stayed began to fear going above the ground again since nobody returned, in the end they try to not speak of it between one another again and start to create a new life for themselves.
Points that might help get answers
construction would start around 2045
It's a large population of around 600k that gets halved to around 300k when cut off from the above world, I would like them to live at depths so far down that the idea of going back up is unthinkable or now to dangerous.
We have the old city's to check over for resources
Being cut off from the surface happens about 80 years after they start construction so we would have better technology to work with
A drug was administered world wide around 2125 which culls off 70% of the population only those that stayed deep underground are not effected
We have massive cities connected to one another so plenty of space after the drug was administered
Thank you all in advance