Well, I would image Teotihuacáno society WAS underpinned by the traders, artisans and especially farmers, since it takes a thriving agricultural community to support such a large urban settlement and we know how extensive their trade networks were. But that doesn't discount the possibility of a high level of militarism either - I don't know, but maybe it was a similar situation to the later Aztecs, who didn't maintain a standing army but as males of all social classes underwent at least some level of military training there was a large body of 'warriors' to draw on for campaigns.

The main reason it was assumed Teotihuacán wasn't very militaristic is the lack of warfare-related symbolism in the city's murals - they don't depict the usual ritual sacrifice and martial themes found in the iconography of other Mesoamerican cites. However, discoveries made by the Feathered Serpent Pyramid Project at the Temple of Quetzalcóatl (1989) of the of sacrificial burials of around 200 individuals, of which many were males buried with military weaponry and attire, revealed human sacrifice and militarism was apparently central to Teotihuacán’s culture at a relatively early stage in the city's history, and on a scale hitherto unsuspected. More recently, excavations also revealed sacrificial burials at the Pyramid of the Moon. These discoveries have forced the traditional iconographic interpretations to be reconsidered from a different perspective.

Anyone interested in the subject might care to read Human Sacrifice, Militarism, and Rulership: Materialization of State Ideology at the Feathered Serpent Pyramid, Teotihuacán by Saburo Sugiyama, who led the excavations and strongly believes "the pyramid commemorated the accession of rulers who were inscribed to govern with military force on behalf of the gods".