The first Inca ruler was Manco Capac. There is no specific date for this ruler nor for the seven succeeding rulers, but the assumed dates are 1250 to 1438. The Inca originated at Cusco in the central highlands and expanded down the coast. The basis of the Inca's conquest is believed to be their organization. Their divine symbol was the sun god, their bureaucratic system consisted of a circle of officials belonging to eleven royal ayllus, and the line of descent continued through incestuous marriage with a sister who becomes the coya or "legal queen." The expansion of the Inca empire probably resulted from climatic conditions. Their resources in the highlands were limited to llama, alpaca, and vicuna.

In 1445, Pachacuti Inca Yupanqui began conquest of the Titicaca regions. He incorporated and developed patterns of cultures already in existence, particularly that of the Chimu. Pachacuti had disciplined officers from his own elite household. Common soldiers were armed with bronze battle axes, wooden hafts with stone or bronze heads, slings, lances, throwing spears, bows and arrows, wooden shields covered with leather, cotton or cane helmets, and quilted armor. In each captured province Inca officials were superimposed upon the existing local officials. The loyalty of the captured province was assured by taking the sons of the officials hostage in Cusco. They made Quechua the official language and sun worship the official religion. They exploited the labor force in order to increase productivity and rapidly develop irrigation and terrace cultivation systems, and used guano deposits found on the coastal islands as fertilizer. The Inca social system required a severe authoritarian government backed by ritual and divine compulsion.

They built temples and fortresses and were supreme in road building. The roads extended 3,250 miles from Quito in the north to Talca in Central Chile. These roads were vital to the maintenance of the empire, but ironically this network of highways made the Spanish conquest easier. There were road markers every topo which is 4.5 miles and rest houses or tambos every 12 miles for the Inca ruler and his retinue. Small post houses called chasquis every 5 miles housed the runners and were used for relaying dispatches at the rate of about 150 miles per day. Verbal dispatches were supplemented by quipu or knotted strings, probably involving a code based on numbers. These were the equivalent of the notched sticks of the old tally system used in Europe.

Inca society was based on the idea of "equal footing." All men had to work in order to live, and even the Inca nobles helped to set an example. However, some archaeologists believe this was a façade supporting a two-caste system. The penalties for breaking the law were less severe for bureaucratic elites; this emphasizes the importance of the upper caste in the maintenance of the system.