Assumed outspring has been an issue of discussion for a long time.

One theory and supported from a certain amount of anthropological findings, are the theory of the Incas to be decendants of a rather poor and non-high cultural tribespeople from the areas around Titicaca and from todays Puno and west towards Cuzco.

They appears like a people without any real importance considering the higher pre-Inca cultures of the time.
One think that from the early 1200 AC, they started expanding territory and began to rule both in and around the Cuzco.
This is however one theory, and in my opinion all Inca history is walking on a very thin ice of presumptions, due to the myths and facts always changing and almost ghosting around anyone trying to get the reality out of the hundreds of tails and myths all over the high Sierras in the Andes.
A few, if any culture ever has been so difficult to get an hold of, like the Incas history.
Another theory is that the Incas came from the high land surrounding Cuzco, but the local myths tells that they came from the islands of Titicaca, more like the first version mentioned above.
But, the theory of the Incas coming from Machu Picchu, like Bingham presumed, is not very dependable, because one presume that Machu Picchu was build in a later Inca period of time.
There are numberless versions crossing into each other all over the Andes area, and nobody can really be sure in anything, most due to the fact that the time...that is the events and years they should have happened never are trustworthy.
We cant follow the line of Inca rulers and be sure it is real persons, especially the first Incas who seems to be legends more than real people.

They stepped into the historic area around the year 1200 A.C. 
However already a lot of pre-Inca cultures was solid founded and developed in the areas which would become the great Inca empire.
One can say that the Incas came to rule over a fully dished table of culture goods already existent and in order.
The Incas started to develop further and expanded the area of their believes, based on these pre-Inca cultural civilizations which they eventually became the rulers over.
The Incas adopted and formed the different cultures into a main path that all lead to the worship of the Sons of God: The Sun, The Inca himself and his earthly temples and priesthood.

All the tribes concurred had to do dutywork (mitas).
This meant that public construction work, often of enormous dimensions, could be done.
One of the most important constructions was roads, but also buildings, temples, and watering systems.
Above all the systematic road construction meant an effective administration of the empire, securing the unity and contact with and between the different areas, from the last outpost to the more stabile and populated cities.

The taxes was very tough but the Incas did however not take the goods for only themselves.
All over the empire it was build public storehouses were crop and life goods were stored, securing against all kinds of hunger and bad crops or bad years in the empire.
Also people who didnt have anything was given supply from these storehouses. The storehouses was controlled locally by the state officials.(The Spanish plundered and finished these storehouses in a short time, causing hunger, poverty and suffering all over the empire.)

The Inca warriors was recruited by offers of plundering, promises to be given new  and better land to live on, and other goods connected to the duty of being the Incas servants.
The organization of military was very systematic. Each "platoon" was divided into groups of ten, hundred and a thousand warriors.
The main force was very skilled and trained, an absolutely capable defence ablility, and a fearsome striking power.

Until these days there has been a misunderstanding that also the civil population were divided into groups after the ten decimal system, but this seem to be the result of early Spanish  History writers and their misconceptions .

The Incas claimed to be the sons of the sun, and divine decendants of the sungod.
They introduced this religion all over the Inca empire, and the consequences was that most part of the public and administrative organs were identical all over the Inca territories.

When the Incas concurred a tribe or city, they destroyed the local gods and their temples, to avoid any resistance.
But, in some cases they preferred to stay friends with gods that were so strong and great that even the Incas let them be...adopting them , their temples and priests into the long path of holy places and customs which the Incas had developed further.
Then the people could continue to seek advice and support from these sources in difficult and important questions, but this time under the Incas rulership.

Even if the local chiefs and administrations could keep their powers to some extent in the traditional ways, the religious and most of the important administrative fields was identical enforced all over by the Incas. One can say it was an imperialistic legislature.
The Incas had the highest juristic  rights, and functioned like judge legistrators in important matters.
The local chief could still be in some power, but the Incas vice-regents (Churucos) had the final word and control over the general administrations.
To make this function properly , it was demanded that all persons in mayor administrations had to speak the official language of Quechua.

The system of roads built by the Incas was, with its restingstations, proviantstoring for the messengers, and the messenger system, built to function like a relayrace, as systematic as anyone can imagine. The Incas didnt have any written language as we know about, and used a system of tied knots called "Quipu".
This way one could count, measure and hold order in different important areas of state administration of goods, labor and more.
The Inca could control the use of resources out in his provinces and make restrictions if necessary.
Corruption and unfaithful servants was a problem, but if it was discovered , the penalty was death.