Just as a fun exercise, I wonder what civs would have the biggest amount of "possible parents"
for simplification let's only consider civs that actually feel sensible to be added to civ7, so no "sultanate of Karaman" or whatever
So far my picks are:
- modern era Ottomans: Byzantium, Abbasids, Seljuks, Gokturks, "Mongols" (I mean Ilkhanate), really any major era II Turkic or Persianate empire you can think of ad infinitum
- exploration era Seljuks or Ottomans: Hittites, Persia, Greece, Rome, Scythians, whatever ancient parents of Turks or Mongols, kinda Assyria, kinda Egypt, kinda ancient Arabs
- exploration era Spain: Iberians, Phoenicians, Celts, Rome, Goths, Berbers/Numidia, kinda ancient Arabs (->Moors->Spain)
But I think that surprisingly enough the strongest contender would be modern era USA (duh): Normans, Spain, England/Anglo-Saxons, Franks/HRE, Netherlands, Ireland, and last but not least literally all native American tribes if you accept this concept as not offensive
hell you can even cram Nordics in there, both in their Viking and non-Viking clothes
EDIT
I think modern India could be one of the very few civilizations capable of matching US regarding the amount of game-worthy civs you can cram in as their sensible ancestors from the previous era...