From The Comanche Empire, by Pekka Hämäläinen (Yale U. Press, 2008), pp. 70-71:
A superb hunting niche framed by two major agricultural spheres—the Rio Grande valley and the southern prairies—the upper Arkansas was primed for commercial prominence. Comanches had capitalized on the Arkansas’ centrality since the 1740s, when they forged exchange ties with the Taovayas and the French in the east. From the 1760s on, however, Comanches increasingly focused their commercial activities to the northern and central plains, where the diffusion of horses had opened fresh commercial opportunities.
The spread of the horse frontier across the Great Plains revealed yet another natural advantage of the upper Arkansas basin: it marked the northern limit for intensive horse husbandry on the continental grasslands. The climate became increasingly adverse for horses above the Arkansas, turning noticeably harsher north of the Platte River and outright hostile above the Missouri. The long and cold northern winters took a heavy toll on foals and pregnant mares, and the vicious blizzards could literally freeze entire herds on their hooves. Such hardships kept most northern tribes chronically horse-poor: only a few groups beyond the Arkansas valley managed to acquire enough animals to meet basic hunting and transportation needs. To the south of the Arkansas, however, winters were considerably milder, posing few limitations on animal husbandry. This meant that western Comanches could raise horses with relative ease and then export them to a vast perennial deficit region—a prerogative that gave them trading power that was rivaled only by the Mandans’ and Hidatsas’ celebrated trading villages on the middle Missouri River.
As the various Native groups on the central and northern plains acquired their first horses around midcentury, they quickly began to look south to Comancheria to build up their herds. In the course of the 1760s and 1770s, western Comanches incorporated many of those groups into an expanding exchange circle. They opened trade relations with the Pawnees, Cheyennes, and Kiowas, who ranged on the western plains between the Arkansas River and the Black Hills, and with the Ponca, Kansa, and Iowa farmers along the lower Missouri, Kansas, and Des Moines rivers. Recent converts to equestrianism, all these groups coveted horses and were willing to travel hundreds of miles to the Arkansas valley to obtain them. They incorporated these trade journeys into their semiannual hunting expeditions, traveling along established trails that led from the Republican and Kansas rivers tot he Great Bend of the Arkansas, which was only a few days’ journey away from the Big Timbers, the favorite camping ground of western Comanches.
While extending their commercial reach into the northern plains, western Comanches continued to trade actively on other fronts. They visited the Taos fairs and restored the ties with the Wichitas that had been severed in 1757 when the Taovayas fled from the Arkansas River. Now traveling to western Comanchería from their new villages on the middle Rad and Brazos rivers, Taovayas traded garden produce as well as high-quality guns, which they obtained from wide-ranging British contraband traders operating out of the numerous British posts that emerged on the east bank of the Mississippi after 1763. As a dramatic example of the volume of this trade, a Taovaya trading party sold seventeen horseloads of guns to western Comanches in a single transaction in 1768. The three-way commerce among Comanches, Taovayas, and British thrived well into the 1770s. According to a 1776 Spanish account, western Comanches received quantities of rifles, pistols, munitions, iron hatchets, and metal utensils from Taovayas, who in turn acquired these goods from the lower Mississippi valley.