The North Sea was inhatibed : https://en.wikipedia.org/wiki/Doggerland
I end up at https://skepticalscience.com/Past-150000-Years-of-Sea-Level-... ( that's right ) :
"During all episodes of major global ice loss, sea level rise has reached rates of at least 1.2 metres per century (equivalent to 12 mm per year). This is 4 times the current rate of sea level rise."
Not relying on one opinion, I view the XKCD of the sibbling : no sources.
Next hit on DDG : https://en.wikipedia.org/wiki/Past_sea_level :
"Observational and modeling studies of mass loss from glaciers and ice caps indicate a contribution to a sea-level rise of 2 to 4 cm over the 20th century. "
Which is very low.
Would you care to back up your statement?
I'm having a hard time parsing that... Are you suggesting the XKCD graph lacks sources?
Even if I think of something like a Nozickian world as a starter, with exchangeable money as a transaction facility for transferring information, I immediately think we would see the roaming "tribes" as something akin to corporations.