When Francisco Pizarro began his campaign to conquer the Incas, he knew from the example provided by Hernan Cortés exactly how to accomplish his goal. Select a Native American god that you perceive to be the most important, and impose yourself upon him. This ploy worked remarkably well with Moctezuma and the Aztecs, and it proved only slightly less effective with the Incas.
We have been told that Quetzalcóatl and Viracocha were white bearded gods who brought civilization to the Native Americans. These gods then disappeared to the east vowing to return someday. However, where any conquest of one group of people over another is concerned we must always remember the old truism of history being written by the victors, and it seems to be quite apt in this case.
It was 1519 and Moctezuma must have been worried, he’d heard the stories from the coast of huge hairy men whose houses floated on the sea, they could make thunder and lightening, they rode monsters, so they must be gods. But which gods, and how could he avoid offending these gods by making a mistake? As Cortés approached Vera Cruz, Moctezuma sent him magnificent gifts, including the traditional garb of Quetzalcóatl, the Rain God and the god known as ‘Smoking Mirror’. 
If indeed Quetzalcóatl was at that time conceived as a white god destined to return from the east (as some modern writers present him), why did Moctezuma send the attire for three separate gods instead of just that for Quetzalcóatl? Why didn’t Moctezuma know it was Quetzalcóatl?
In Voyagers to the New World, Nigel Davies explains:
The assertion that Quetzalcóatl was white and that he was destined one day to reappear can be traced not to native sources but to Hispanized chroniclers, whose references to the subject are vague. Fray Motolinia, writing between 1530 and 1546, tells of a god of the wind called Quetzalcóatl, who came from Tula and would one day return. Fray Mendieta, towards the end of the sixteenth century, repeats the same tale, but improves upon the original by adding the detail that he was white as well as bearded. Alva Ixtilxóchitl, writing even later, repeats this but with the added refinement that Quetzalcóatl was expected to come back in the year I Reed. However, the native sources, written in Nahuatl, say nothing about Quetzalcóatl returning – except as the Morning Star.
Writers continue to harp on the Spanish accounts of the white god who was destined to come back one day. People unaware of the deep vein of symbolism permeating ancient Mexican thought may be impressed by such a story. But both Alfonso Caso and Hermann Beyer, foremost among scholars versed in Mexican religion, ridiculed the notion. They both rightly insisted that more often than not Quetzalcóatl is depicted as wearing a strange duckbill mask, an integral part of his attire as god of the wind. When, however, the deity appears in codices without this adornment, then invariably his face is totally black (the symbolic colour of priests), or else it is black with vertical yellow stripes. So much for the ‘white’ god. 
From his three choices Cortés selected the garb of Quetzalcóatl and the Spanish Imposition began. Legends of civilizing white gods returning from the east are the creations not of native Americans but of Spanish conquerors, crude adaptations of native stories to assist in and legitimize the process of conquest.
The Spanish found the native practice of human sacrifice quite uncivilized and needed as much leverage as possible to force the native population to convert to the Catholic Church. This need forced the change from bloodthirsty god (often depicted holding a huge thorn for bloodletting) to a Christ-like civilizer, wandering the countryside and robed in white.
In Heaven’s Mirror Graham Hancock makes this statement:
It is one of the great unexplained puzzles of Central American history that the murderous Aztecs worshipped and honoured this benign figure in all manner of rituals, and always spoke with awe of his peaceful and life-giving ways. They believed that he and his followers had been driven out of Mexico long ages previously, but that they would one day return, coming from the west, by boat. They also believed that Quetzalcóatl would punish them for having reverted to human sacrifice, that he would put an end to evil and fear, and that he would restore the golden age of peace and plenty over which he had presided in the mythical past. 
However there is no unexplained puzzle, the answer has been available for a long time as Nigel Davies explains:
Hispanized accounts credit Quetzalcóatl with a revulsion against human sacrifice. But other sources describe the mammoth sacrifice – reputedly of eighty thousand victims – which took place in the Aztec capital thirty years before the Conquest, and in which priests dressed as Quetzalcóatl played a leading part. To appreciate the pitiless nature of the Indian god before he was whitewashed (in every sense of the word) a glance at the Codex Borgia will suffice. There Quetzalcóatl is displayed in the not very Christian gesture of gouging out the eye of a wretched little captive. In this drawing he wears his characteristic red and black duckbill mask and a beard of yellow ochre feathers. (When in the same codex, he is depicted without his mask, the god normally has a black face, sometimes with a yellow nose, and in some cases with a red mouth). 
The difference between Quetzalcóatl the Native-American god and Quetzalcóatl the Spanish god can also be seen at his pyramid, the Feathered Serpent Pyramid at Teotihuacan where the graves of sacrificial victims , dating to the time of the pyramid’s construction, have been discovered.
The most authenic account of Quetzalcóatl’s departure comes from the Annals of Cuauhtitlan and was written in the Nahuatl language. The story is vastly different from the hispanized Quetzalcóatl legend:
Tula, a Toltec city in central Mexico, was torn with internal strife and bickering. The god Quetzalcóatl became convinced that the city was doomed due to his great age. This idea was reinforced when rival gods showed him his face in a mirror now wrinkled and unattractive. Quetzalcóatl adorned himself in his feathers and mask, went to the sea-coast, and by his own hand set himself on fire. He spirit rose with the smoke into the heavens and became the star which appears in the morning. 
Fourteen years later Francisco Pizarro, who before becoming a soldier was a swineherd, teamed up with a more experienced soldier and with only a small handful of Spanish conquistadors set out to conquer the lands to the south. Years before Pizarro had heard these lands were rich in gold and precious stones. But they were few, and the Inca were many, so how could they expect to conquer such a nation?
One of the methods used once again was the Spanish Imposition of an important god. The native Americans did not at first think of the Spanish as Viracocha. The Spanish, to win the support of certain Indians, told them that they had been sent by Viracocha and that they were his sons. From that point, as in Mexico with Quetzalcóatl, you can follow the Spanish chroniclers as the legends of Viracocha began to be changed.
Now we begin to see a very Catholicised version of Viracocha emerge; he traveled the countryside healing the sick and the blind, preaching repentance, wearing a long white beard and robe. Quite often Viracocha is likened to certain Saints including St. Thomas and St. Bartholomew. 
But as Evan Hadingham in Lines to the Mountain Gods: Nazca and the Mysteries of Peru states:
As for the intriguing detail of Kon-Tiki’s (Viracocha) white and bearded appearance, these same sources indicate that his “whiteness” stood for the dazzling light of the sun. In addition, the many-sided aspects of the god included a “junior” and a “senior” sun; these different solar identities were evidently linked to the progress of the sun through the sky during the seasons. Viracocha was particularly associated with the mature, aged sun of midwinter, a time when the sun’s rays are at their feeblest; hence the appropriateness of the bearded image. Moreover, within recent memory, the Aymara speakers of the Titicaca region used to refer to the sun’s rays as his beard. 
Many of the Spanish versions of Viracocha include the story of a statue in Cacha of him depicted as a white man with a long flowing beard dressed in a white robe. The statue was claimed to be ‘proof’ of the Spanish version. However, only one Spanish chronicler, Cieza de León, recorded that he had actually seen the statue, and he wrote that the idea was nothing but a bad joke. Another chronicler, Garcilaso de la Vega, recorded the strange destruction of the statue at the hands of none other than the Spanish themselves. Why destroy your proof? Unless, of course, it is not proof.
Today, this Spanish Imposition continues in the form of writers who do not look past the Hispanized versions of these gods to the original codices and sources and see the original Native American Indian gods behind them.
Evan Hadingham summed this up well when he wrote:
Not a shred of genuine evidence, anatomical or otherwise, supports the notion of an alien race present in ancient Peru. Nevertheless, many popular writers still assume that the native Peruvians were incapable of developing civilization on their own without the aid of voyagers from afar. Dozens of different candidates have been proposed for these enlightened mariners. These have ranged from the Lost Tribes of Israel to the people of Atlantis, not to mention the early Chinese in their junks, and reed-boat sailors from Africa. 
Compounding the problems created by the Spanish Imposition on the Viracocha legend are the Incas themselves. The first great warrior King, Pachacutec (or Pachakuti) may have contrived much of Inca legend including the Viracocha creation myth. In The Incas Nigel Davies explains, ” In this instance it seems that we are faced not with primordial mythology but with myth manipulated and modified to serve the ends of state and empire.” 
The legends of Quetzalcóatl and Viracocha as white civilizing gods are not native in origin and can not be used to argue for supposed historical events long ages ago. The Spanish, who saw themselves as white civilizers, clearly imposed such legends on native peoples to aid in their conquest. To base your arguments from such legends then is incorrect and an example of how selective presentation of evidence is not the proper “method” in making historical arguments.
 Voyagers to the New World
Nigel Davies, Macmillan London, 1979
 The Ancient Civilizations of Peru
J. Alden Mason, Penguin, 1957 Reprinted in 1991
 Lines to the Mountain Gods: Nazca and the Mysteries of Peru
Evan Hadingham, University of Oklahoma Press, 1987
 Kingdoms of Gold, Kingdoms of Jade
Brian M. Fagan, Thames and Hudson, 1991
Valley of the Spirits
Alan L. Kolata, John Wiley & Sons, 1996
 Heaven’s Mirror
 The Incas
Nigel Davies, University Press of Colorado, 1995