There may not be an answer. There are, however, certain facts that one cannot overlook. The mixture of meat, beans, peppers, and herbs was known to the Incas, Aztecs, and Mayan Indians long before Columbus and the conquistadores.
Fact: Chile peppers were used in Cervantes's Spain and show up in great ancient cuisines of China, India, Indonesia, Italy, the Caribbean, France, and the Arab states.
Fact: Don Juan de Onate entered what is now New Mexico in 1598 and brought with him the green chile pepper. It has grown there for the nearly four hundred years since.
Fact: Canary Islanders, transplanted in San Antonio as early as 1723, used local peppers, wild onions, garlic, and other spices to concoct pungent meat dishes - improvising upon ones they had cooked for generations in their native land, where the chile pepper also grew.
Exit fact, enter conjecture.
There is little doubt that cattle drivers and trail hands did more to popularize the dish throughout the Southwest than anybody else, and there is a tale that we heard one frosty night in a Texican bar in Marfa, Texas, about a range cook who made chili along all the great cattle trails of Texas. He collected wild oregano, chile peppers, wild garlic, and onions and mixed it all with the fresh-killed beef or buffalo - or jackrabbit, armadillo, rattlesnake, or whatever he had at hand - and the cowhands ate it like ambrosia. And to make sure he had an ample supply of native spices wherever he went, he planted gardens along the paths of the cattle drives - mostly in patches of mesquite - to protect them from the hooves of the marauding cattle. The next time the drive went by there, he found his garden and harvested the crop, hanging the peppers and onions and oregano to dry on the side of the chuck wagon. The cook blazed a trail across Texas with tiny, spicy gardens.