I just started playing the Kingdoms expansion. I am playing the America's as the Apache. My first vilage started with a population of ~600 people. I moved the mouse over the population and it said the villiage would upgrade when i had 800 people. I now have 943 people, but have not been able to upgrade, and now when I mouse over the population, it doesn't say anything. I have every single building built and there arent any more to build.
Is there something different with the Indians tribes for upgrading villages/towns?
That just means that it should take some time for the upgrade to be invented. You see, the Apaches are a rather adaptive tribe and should get this technology before other tribes; Goes the show you why they have cavalry in the later turns, while other tribes are still scrambling for light infantry. You see, in Eourope ideas flourished while in the Americas ideas had to be encouraged.
I've only played Spain in that campaign and you get more innovations and such as you conquer more territories. So I would think the same would apply in your case. Keep getting more regions and you'll probably gain more technologies.
I was not able to build any horse units even when I had 4500 people in one village. If you have seen apache horse units, there must be further updates to come, but I dont know for sure. I am going to start a new campaign later and try to expand just to see if that makes a difference.