For the Incas, the army was the chief tool for expanding the empire's borders. It was also an important safeguard against threats from outside and from within the imperial domains. Indeed, warfare was common among the Incas.

For those fulfilling their mit'a duty, serving in the army was the riskiest way of discharging their tax obligations. There was always the threat of being severely wounded or killed in battle. Plus, campaigns could stretch into years. The Sapa Inca Atahuallpa, for instance, before becoming emperor, led troops on a campaign against Ecuadorian rebels that lasted almost a decade. The rewards of a successful campaign, however, were great. Even common soldiers could expect to receive valuable cloth— if not more lavish presents—as gifts from a grateful emperor.

Organization of the Army

The smallest unit in the Incan army had ten soldiers under the leadership of...