Make a unique district (but not encampment) or a unique building (but not barracks) I guess.

@太慢鱼龙 thanks for your comment. Essentially, it would help the Incas be more generalists, but in reality, there isn't a specific unique building or district that truly stands out. At best, one could consider the 'qullqa' (large state food storage facilities), but it isn't very different from a granary. What stood out the most were precisely their distributive labor policies (mita) and large state structures, like the 'Qhapaq Ñan' road network. That's why I believe that, for the sake of historical accuracy, their unique traits should lie in those areas. I would also like to know what you think about the current design of the civilization and where you believe its weaknesses lie.