To begin with, I would like to point out everybody who has posted previous to me are complete idiots and wannabe historians that don't know a crap about what they are posting about the Incas. I will now refute the stupid statements made by several forumers...
The Incans were lazy
Lesson 1: The Incas were anything but lazy. Lazyness was a capital crime in the Tawantinsuyu (Name of the "Inca Empire"). In fact, work was to the Incas almost like their leisure time since they did what they were good at and did it to survive. The Inca empire was practically much like those of a bunch of working ants, and that's how it expanded so rapidly.
Haha wikipedia? First, you make the mistake of referring me to Wikipedia. Fifty percent of the time, it is misleading or inaccurate.
Lesson 2: According to recent studies, Wikipedia is a very reliable source since moderating and controlling of what users have been making has been greatly enforced. Not only that, but Wikipedia was rated nearly as reliable as other famed encyclopedias, such as "Brittanica."
Thats because the Aztecs were idiots and they like to dress and prepare for war like jaguars...
Lesson 3: Yes, the Aztecs did stupidly dressed up for warfare because they tought they would "gain" the spirit of the animal they were in. Yet, their stupid dresses were in fact very helpful since they could camouflage with them and they looked quite scary when fighting against other tribes (like Halloween parties). One of the most horrible things I saw was from the Zapotec priests, whom wore the skin of other human beings.
Gold has nothing to do with a nation being greater than another.
Lesson 4: Correct, back in the times of Pre-Columbian America, gold really had little impact for the civilizations since there was no currency. Nevertheless, the Incas did have much more gold and silver than the Aztecs could have even ever dreamed of.
Uhh how? when the Aztecs stood a greater chance against the Spanish?
Lesson 5: The Inca Emperor, Tupac Inca, was assassinated and his son Huayna Capac took the power of the empire. Huayna Capac had various sons, but his favorite was Atahualpa. Huayna went on a conquering spree in the northern South America, but was frustrated on his efforts upon learning of "strange bearded men" arriving at the coasts--so he had to investigate on the situation. Unluckily for him, these men brought disease with them and in time Huayna Capac got sick with smallpox and died. Ninan, Huayna's next-in-line for the Inca throne, also died of smallpox since he was with his father in the north.
Atahualpa, favorite son of Huayna, gained the recently gained sections of the Inca Empire and the valley of Cajamarca. Huascar, the next legitimate heir to the Inca empire, wanted the whole empire and did not think Atahualpa deserved to inherit anything. Thus, a civil war erupted amongst the Incas, with the Inca generals supporting Atahualpa, and the nobles of Cusco supporting Huascar.
In time, this war devastated the Inca empire. The Incas used up all of their strength and tactics fighting amongst themselves, and smallpox slowly kept advancing throughout the empire. By the time Pizarro returned with a force to conquer the Incas, he found an empire devastated by disease (smallpox), torn apart by civil war, and completely weak internally.
Incas were a civilization that started lately, and of course they hadnt got so much power as aztecs did
Lesson 6: The Incas were a civilization that was much older than the Aztecs. The Incas started as a very weak kingdom in the Andean highlands, but in time, with good rulers, strong armies, and smart alliances, the Incas became the strongest civilization in America.
The Inca empire was an efficient and productive empire. The Incas found it easier to completely control other tribes and help them become strong in such a manner that would be beneficial to the empire as a whole (reason as to why the Incas are commonly said to have been pro-Socialistic) and thus the people.
The Aztecs? They kept little states under their control so that they could gain people to sacrifice after fighting fake battles. That's not being productive at all, the Aztecs were more like a virus that hurt the other Meso-American nations. The only good thing the Aztecs made was Tenochtitlan, because other than that the Aztecs were a bunch of war-like monsters.
Sure, the Aztecs had a respectable army and a powerful force, but they didn't use that to do good. The Aztecs needed a strong army because otherwise the other tribes in the area would have kicked their butts since the Aztecs were perhaps one of the most hated tribes in the area (Hence the many allies Cortez gained).
On the other hand, Pizarro only got support from certain tribes within the Inca empire, specifically those that had recently been conquered. The Inca empire wasn't able to immediately attack the Spanish because Pizarro tricked the Incas into a peaceful situation. The Inca emperor was caught, several generals were killed, and the Incas had to thus re-build their forces and their plans.
They kicked Spanish ass while Incas were decimated
Lesson 7: The Incas, in time, rebuilt their forces with the aid of the "new" emperor, Manco Inca. Manco secretely built an army to fight the Spaniards, whom were arguing amongst themselves. The Incas thus struck back at the Spanish, when they least expected (much like the Spanish did to the Incas), and with Manco at the head they took back several towns and villages. The Incas did beat the Spanish in several battles, and all the Spanish could do was retreat back into Lima (the Spanish stronghold).
The Incas even went as far as to siege Cusco, and the city itself was to once more become Incan had it not been for an amazing strategy used by the Spanish (Whom had united once more after Pizarro and De Almagro got killed by their respective allies) that barely got them to beat the Incas. The Inca troops retreated not because they lost the siege, though, but because they were being decimated by disease!
Even still, the Incas retreated into Vilcabamba and continued their raids and attacks against the Spanish.
What did the Aztecs do? After "La Noche Triste" and a series of minor battles which the Aztecs won, Cortez soon returned and kicked Aztec butt as rapid as the Aztecs had to the Spanish. Not only that, but soon after the Aztecs didn't last at all. For the least the Incas were able to retain their power and continued to rule over Vilcabamba and kept on fighting, but the Aztecs were taken out and there was no comeback for them.
Inca didn't do much great except for maybe the fortresses they built, in which were useless against Spanish forces.
Lesson 8: Ever heard of Macchu Pichu, one of the new 7 wonders of the world??? Then there are also amazing sites like Ollantaytambo and Tambo Colorado, then Sacsayhuaman and Cusco itself (Allegedly being "Puma shaped").
The actual reason why the Aztec lost was because their food supply got cut off and the Spanish surrounded their allies.
As correct as that may be, the fall of the Aztecs was going to happen sooner or later. The other tribes in the area disliked the Aztecs, so if the Spanish wouldn't have given them the blow of grace, then another tribe would have taken out the Aztecs.
This similar situation came for the Incas. Had the Spanish come at an earlier time, then their armies wouldn't have been able to even make it past the coast. Yet, the Spanish came at a very unsuitable moment for the Incas, a time when the might of the Inca empire had been destroyed by the Incas themselves.
NEVERTHELESS, the Incas would have still made a very good civilization for the game because they were the strongest in America (Along with the Aztec), economically better (Nobody beat them at that), and had a very unique form of government. The Incas should have been a civilization, and ES should at some point or another try to include them in one of their Age of Empires games with the main reason being because the Incas were an actual empire.