The Hisatsinom (known incorrectly in our own timeline as the Anasazi cliff-dwellers) are an urban culture, with fortified cliff cities and advanced infrastructure. Much like Dwarves in many classic fantasy settings, they're perfectly content to barricade themselves in their cities and ignore the rest of the world. They have strong defensive forces, but not much active military. There was a vague suggestion of drider soldiers, and I sort of tied it back to the skinwalker idea by suggesting enchanted monstrous spider exoskeletons that a warrior could climb into to give them the ability to walk up and down the sheer cliff faces and spin webs while they could still do their normal warrior stuff with their arms.
To fill the gap outside their cities and solve the problems of banditry by hungry apachean tribes, the Hisatsinom high priest struck a treaty with the Apachean tribes of the southwest. The treaty set up a framework to grant the Apachean tribes access to Hisatsinom cities and supplies, in exchange for service as a sort of mercenary military force. Like watch dogs, the Apachean tribes patrol the areas between the cities, keep the Web Below safe from bandits, and fight off or warn of threats that come too close to the cities. The exact details of the arrangements were of course left to the negotiations of the individual cities.
In the last fifty years, though, there's been something of a wrench in the works, in the form of the Great Basin tribes, driven south when the little folk nation drove them out. Banditry returned, the Apacheans didn't like the idea of new competition for their comfortable positions, and nobody really knew what to do with the refugees. In the years hence, the Hisatsinom have struggled to assimilate them, trying to shuffle and train them into a more serious military force, to try and use them as a front line to fight the advancing Mexica. Some are reluctant to arm and train these newcomers, fearing a shift in power, but this mistrust seems to make the problem worse than arming them did.