The Inca people began as a tribe of the Killke culture in the Cuzco area around the 12th century AD. Under the leadership of Manco Capac, they formed the small city-state of Cuzco (Quechua Qosqo).
The first step in the expansion of the Inca Empire was the defeat of the Hanan Chankas, a group that lived in the departments of Ayacucho and Huancavelica, near Cuzco. Thatallowed them to control a large territory around Cuzco and incorporate its population into its army. The expansion continued to the Lake Titicaca region where they allied with the Lupaca ethnic group to defeat the powerful Hatun Colla. The Incas had a special interest to control this region due to their abundant natural resources. After his military victory, Inca Pachacuti rebuilt Cuzco. 
In1438 AD, under the command of Sapa Inca (paramount leader) Pachacuti, much of modern day southern Peru was conquered. Cuzco was rebuilt as a major city and capital of the newly reorganized empire. Known as Tawantinsuyu, it was a federalist system, consisting of a central government with the Inca at its head and four provincial governments with strong leaders: Chinchasuyu (NW), Antisuyu (NE),Contisuyu (SW), and Collasuyu (SE). The powerful Inca emperor is also thought to have built Machu Picchu, either as a family home or as a vacation retreat.
The Incas conquered a vast territory using reciprocity or alliances. Pachacuti would send spies to regions he had wanted in his empire. They would then report back on the political organization, military might, and wealth. The Sapa Inca would thensend messages to the leaders of these lands, extolling the benefits of joining his empire. He offered gifts of luxury goods like high quality textiles,coca leaves and mullu and promised that all living in those territories would be materially richer as subject rulers of the Inca. Most accepted the rule of the Inca as a fait accompli and acquiesced peacefully. The neighboring rulers' children wouldbe brought to Cuzco to be taught about Inca administration systems, and then would return to rule their native lands. This allowed the Inca to indoctrinate the former rulers' children into the Inca nobility, and, with luck, marry their daughters into families at various corners of the empire. If they did not accept the alliance they used force to subdue the tribe and since the Incas had a morepowerful military force they always succeeded. The local leaders were executed to secure loyalty among the population.
When the Inca won new territories they moved groups of leaders around to ensure loyalty. A trusted leader would be relocated to a newly conquered territory while those less loyal would be relocated where someone could keep an eye on them. In order to keep in touch with all thecorners of the empire the Inca Empire had a network of messengers known as chasquis.
It was traditional for the Inca's son to lead the army; Pachacuti's son Túpac Inca began conquests to the north in 1463, continuing them as Inca after Pachucuti's death in 1471. His most important conquest was the Kingdom of Chimor, the Inca's only serious rival for the coast of Peru. Túpac Inca's empire stretchednorth into modern day Ecuador and Colombia, and his son Huayna Cápac added significant territory to the south. At its height, Tahuantinsuyo included Peru and Bolivia, most of what is now Ecuador, a large portion of modern-day Chile, and extended into corners of Argentina and Colombia.
Tahuantinsuyo was a patchwork of languages, cultures and peoples. The components of the empire were not all uniformlyloyal, nor were the local cultures all fully integrated. For example, the Chimú used money in their commerce, while the Inca empire as a whole had an economy based on exchange and taxation of luxury goods and labor. (It is said that Inca tax collectors would take the head lice of the lame and old as a symbolic tribute.) The portions of the Chachapoya that had been conquered were almost openly...