The Comancheros were primarily Mexican traders in northern and central New Mexico Territory who made their living by trading with the nomadic Great Plains Indian tribes, in northeastern New Mexico and West Texas. Comancheros were so named because the Comanches, in whose territory they traded, were considered their best customers. They traded manufactured goods (tools and cloth), flour, tobacco, and bread for hides, livestock and slaves from the Comanche. As the Comancheros did not have sufficient access to weapons and gunpowder, there is disagreement about how much they traded these with the Comanche.
Prior to the coming of the Spanish, with their horses, into the American Southwest, with early explorations beginning in the 1540s and permanent settlement in the late 1590s, the people who came to be known as Comanches did not live in the Southern High Plains. The Comanches, a Shoshonean people, migrated from the North and arose as a separate and distinct tribe in the early 18th Century, largely as a result of having obtained breeding stocks of horses after the Pueblo Revolt of 1680. They migrated southward through the Rocky Mountains and into the Southern High Plains, where they and their Shoshonean kinsmen, the Utes, began to appear at trade fairs in Taos about 1700. During the first half of the 18th Century the Comanche gradually spread their area of occupation throughout the Southern High Plains and large areas of Texas, where they largely displaced the tribal peoples who had lived there prior to the coming of the Spaniards, mostly the Apache, who were themselves an earlier migrant group of Athapaskan peoples from the North.
In 1719, the Comanches made the first recorded raid for horses upon the settlements of the Rio Grande Valley. For the next 60 years, the relations of the Comanches with the Spanish and Pueblo settlements was a patchwork of alternate trading and raiding, with different bands being sometimes at peace and sometimes at war with the settlements along the Rio Grande. During the mid-18th century (1750–1780), the plains tribes, notably the Comanche, but also the Apache and other tribal groups, raided the Pueblos and Spanish settlements for horses, corn and slaves with ever-increasing frequency. This continued until 1779, when a 500-man army led directly by the new young governor, Juan Bautista de Anza, and including 200 native auxiliaries, undertook a punitive expedition against the largest and most active group of Comanche raiders, who were led by a man known as Green Horn (Cuerno Verde), and, surprising the Comanches in their camp, killed Green Horn and dealt a severe defeat to the Comanches. This show of force resulted in various Comanche war leaders acceding to peace over the next several years. By the end of 1785 all, or substantially all, of the Comanche bands had agreed. On 28 February 1786 at the Pecos Pueblo a treaty between the Comanche and the Spanish in New Mexico was signed between Governor de Anza and Ecueracapa, a Comanche war chief who had been selected as a plenipotentiary for the Comanche nation.