The central-Andean empire that pioneered the administrative grid and road network the Inca would later inherit.
Its provincial centres were abandoned by ~1000 AD; the political vacuum opened the way to the regional kingdoms the Inca would conquer.
The Wari empire and its administrative network within a survey of ancient South America.
The Wari precedent for the Inca road and administrative system, discussed in this history of the Incas.