Encyclopedia of the Incas

Suppression of revolts provided the empire with the opportunity to consolidate
its administrative power, establishing networks of roads, way stations, and
administrative centers that could facilitate the movement of information from
provinces to the capital (and of soldiers to hot spots that developed). The Incas
demilitarized their interior, except for key facilities, such as bridges. Topa Inca
Yupanqui is generally acknowledged as a great consolidator in the central
highland provinces, but he followed his campaigns of reconquest with an
extended foray into the southern periphery of the empire, bringing some form of
Inca rule to a huge territory that covers parts of what is today southern Peru and
Bolivia, northern Chile, and northwest Argentina.
Inca military strategy developed as conquests extended into the northern
Peruvian highlands and into Ecuador. The broken terrain and climate of the
tropical highlands made it more difficult to divide and conquer local populations,
and the Chachapoya and Cañari peoples proved to be especially difficult to
incorporate. The empire restructured new provinces, resettling much of the
indigenous population and drawing large numbers of permanent retainers
(yanacuna), as well as households that served in a more permanent capacity as
soldiers (see Labor Service). As the Inca advance slowed, the empire shifted
from conscript armies to a standing frontier force, as well as strategically placed
garrisons that protected the corridors from the highlands to the Amazonian slope
(see Fortifications). There is archaeological evidence that local populations also
built frontier forts to protect themselves from the Inca advance, and many groups
were feared for their ability to penetrate Inca territory and wreak havoc on
colonist populations that settled to consolidate imperial power. The emperor
Huayna Capac spent decades living at the front to direct territorial expansion
northward, moving his family there and establishing palaces and estates for their
maintenance.
Accounts of the Inca army in the decade before the Spanish conquest describe
a force that was unlike the army that set imperial expansion in motion, and the
imperial motivation for conquest reflects a different set of targets. Instead of
seeking local allies who led local populations that were at least partly
autonomous, the Incas sought to push “uncivilized” frontier populations out of
territory that the army held as new settlers colonized the land and took over
broader economic networks. This militarized emphasis on civilizing the
Amazonian and Ecuadorian frontier contrasts with the evidence for military
action against the states and empires that ruled over the central and northern
Peruvian coast.