MOO1 started it all, end of story. 
But more seriously, there is indeed a pattern in how the entire RTS4X pool of games flooded the hardcore gamers market; someone out there figured out that the multiple concepts or gameplay contexts had clear potential.
Remember Doom? How many other developpers went down the FPS road to grab a slice of that pie since? CounterStrike or Crysis being just two from a list of many more, recent enough.
And yet, Doom wasn't there first!
So that tells you about GalCiv and if it can actually be matched with other titles throughout its own History.
Plagiarizing is a different issue; but i don't see any particular difference between WoW & Demigod as it pertains to 'situational features', between MoM & Elemental as 'fantasy context', between Chess & Risk & Civilization as being complex or simplistic 'board games', and so on.
It's just that GC2 has a knack for Sci-Fi & space conquest that nobody had ever done in such a sweet & slick manner - differently than others of the same kind.
(PS; CmdoColin, many thks for the links -- it sure brought back memories when i was an early member of Apolyton back in Nov'00!)