For North America, i agree with you the numbers don't tend to match elsewhere. (However, they have tended towards upward revision for 150 years now so who knows?) The interesting thing about these statistics however, is both Mexico and the Andes as regions within continents can compete on population terms with the rest of the world, yet they have 3 civilizations between them
If we're gunna get into statistics, i'll first put this suggestion out there as i hinted at in my first post. The population at large of the continent is irrelevant. If there are interesting civs to be added, add them. You can have incredible civilizations that thrived on low populations, that's not a problem.
Secondly, Cahokia grew to somewhere in the region of 15-30,000 as a metropolis. That's is up there with the largest cities of Europe in the 11th century. In fact the only one notably larger in Europe is the very one you've been so avidly against, Venice
And finally, i know Cahokia and Pueblo may not be realistic but a man can dream! As much as i love hearing an echo, I had in fact mentioned that it my own post
I really get sick of people spouting this:
Secondly, Cahokia grew to somewhere in the region of 15-30,000 as a metropolis. That's is up there with the largest cities of Europe in the 11th century.
Yes, 15-30 thousand in c. 1200 AD is a similar size to some notable European cities at the time, normally cited with London (~20-50k at the time) and Paris (~80k+ at the time). However, cities of 15-30k are not particularly notable historically, and this comparison is more for a modern audience to realise that this city was quite large, and to give it context in a World where cities smaller than 500k are considered small and where cities in excess of 20 million people exist. A singular city of 15-30k however (the estimates range widely from about 6-40 thousand for Cahokia at it's peak) is hardly that impressive in and of itself, and including it as a Civ on it's own is down right impossible before even taking into account that we don't know enough about the people and culture to create such a Civ. Any such Civilization would be a blob Civ, and one based on very limited information at that. Not to say that they as a culture aren't interesting and important, but rather they neither demand inclusion nor is there enough to really base a Civilization around, much like the Indus Valley situation.
As for historical context, and what really annoys me about citing the size of Cahokia, here are some large cities from around the world circa 1200 AD (some, like Venice, Paris and Polonnaruwa are included for flavour and context of their respective regions):
Polonnaruwa - Sri Lanka - ~75,000
Paris - France - ~80,000+
Hangzhou - China - ~350,000-1,000,000+
Angkor - 200,000-1,000,000
Cairo - Egypt - ~250,000-300,000
Fes - Morocco - ~250,000
Bagan - Burma - ~180,000
Baghdad - Iraq - ~150,000-1,000,000
Venice - Venice - ~45,000+
Milan - Lombardy - ~150,000+
Kaifeng - China - ~1,000,000+
It is particularly worth noting that Sri Lanka, Burma and Khmer are not represented within the game, yet have cities even in the era of the height of Cahokia which are far larger and more impressive.
As for other periods of history, there have been 1,000,000+ population cities throughout history, in Xian in around the 7th-9th century had hit around that mark, as had Baghdad (even pushing higher than 2 million during the 7th-9th centuries by some estimates) and Hangzhou at various times, and Kaifeng of course.Constantinople was push toward half a mil around the fall of Western Rome and the early "Dark Ages".
During the classical era of course cities like Alexandria, Antioch, Athens and of course Rome (which at it's height had a population around 1 mil) were huge as well, with populations in the hundreds of thousands right up to around the million range.
In the earlier periods there were still cities in excess of 100,000 such as Babylon, Athens, Xian and Qufu and as far back as 1200 BC Pi-Ramses is estimated to have had a population around 160,000.
Even in the Americas there are far better examples than Cahokia, but it was merely a case of it being impressive for it's context, particularly as it was abandoned before the end of the pre-Columbian age. Other such lost cities such as Tiwanaku are interesting, but again, there are too many issues to consider it to be demanding selection, and having a population of even 40,000 (the wildest estimates I can find) don't even put the city on the sort of scale in terms of the World then or historically that people seem to suggest.