The Aztec Civilization

The Aztec Civilization: What was it like?


You've probably heard of the Aztec civilization, but if you're like most people, there's a good chance you don't know a lot about it.



This Native American state ruled a large portion of the area that is now Mexico, between about 1428 and 1521.








The empire ended when the area was conquered by the Spanish.

However, this empire is not the homogeneous civilization that you might think of at first. The Mexica formed the head of the empire, and built their capital city of Tenochtitlan where the present day Mexico City is located. Even the Mexica were not culturally homogeneous - some researchers believe that as many as seventeen ethnic groups were among the original tribes that came south to the site of Tenochtitlan.


Organizing a Civilization


They originally formed an alliance with two other cities in the area, called Texcoco and Tlacopan, called the Triple Alliance. However, Tenochtitlan eventually became the most powerful, and began conquering other cities. Cultures in the area at the time the Mexicas arrived in the valley of Mexico included the Tepanecs, Cholcos, Xochimilcos, Tlaxcalans and others, all attempting to gain ascendancy in the valley itself.

Each state in the empire was ruled by its local government, which paid tribute and followed a number of laws dictated by the Triple Alliance. Most of the tribute went to Tenochtitlan, since it had most of the power. This type of empire is called a hegemonic or informal empire.

The territories ruled by the Aztec civilization weren't entirely connected, either. Since some city-states successfully resisted, maps of the Aztec empire often have "holes" in them. This doesn't appear to have affected the strength of the empire, however.

Had Europeans not appeared, the empire may have kept on growing. At its height, the Aztec civilization reached east and west from the Pacific Ocean to the Gulf of Mexico. North-south, the empire stretched from Central Mexico to modern day Honduras, El Salvador and Guatemala.




Ruling an Empire


Groups of families were the basic unit of government in the empire. These groups, called calpulli, had existed long before the Aztec civilization, and were set up to own land. The leaders of the calpulli set up schools for common citizens, collected taxes, and took care of basic group needs. Later calpullis were less family related and more regional, but operated in much the same way.








Leaders of the calpullis formed a city council - possibly the unit with the most power in the ancient Aztec government. Each city council had another council within it - an executive council made of four members. One of them would be the leader of the city, or tlatcani.

The council of Tenochtitlan led the empire itself, and has been compared to the senate of Rome. The leader of this group was the Huey Tlatcani, or the emperor. He was worshiped as a god, and had the support of the city council, major government officials, and the priesthood. The most famous of the Aztec emperors was Montezuma II, ruler when Cortes reached the Aztecs.

The famous human sacrifices of the Aztecs were originally infrequent, grotesque to modern eyes. It seems that, during the mid fifteenth century, a series of natural disasters convinced the Mexica that massive sacrifice was needed to satiate their gods. These practices were among the excuses that the Spanish used to attempt to destroy the empire so completely.


The remnants of the Aztec Civilization


Many people in Mexico today can trace their ancestry and some culture back to the Aztec civilization, including the language of the empire (Nahuatl) which is still spoken. If you visit the country today, you'll see a lot of relics of Aztec culture there, including elaborate stone architecture, pottery, jewelry, paintings and more. Place names, religion - even ways of thinking that were seen in the Aztec civilization are still very much a part of Mexico today.

Note: The image on this page is a mechanical clock based on the Aztec calendar of ancient times. It is on display on the grounds of the Roman Catholic Basilica in Mexico City.






Ancient Aztec Government


Ancient Aztec government got its structure from units of society that existed long before the Aztec empire was founded. First, of course, was the family unit, as a basic structure of society. The government was built up from there. Let's take a look at how the government was formed...


The Calpulli


After the family, the basic unit of ancient Aztec government was the calpulli. Families didn't individually own land, the land was owned by a group of families, the calpulli. This structure of local government existed long before the Aztec empire. The leadership in the calpulli would be responsible for the basic needs of the group. They would set up the telpochalli, a school for common citizens. They were also responsible to make sure taxes were collected from the group.

In the cities, calpullis became less family-related and more regional. As is the case today, city life brought many different individuals of different race and culture together.




Nobility and Councils


The nobility and priesthood had a lot of power in Aztec society. But although the nobility provided leadership, they weren't automatically put in government positions. In the cities, each calpulli would have a leader, and those leaders would form another council. It was the city councils that held a lot of power in the ancient Aztec government.

By the early-mid 1400s, three powerful city-states had formed the famous Triple Alliance in central Mexico. These cities were Tenochtitlán, Texcoco, and Tlacopan. These cities dominated central Mexico, and it was Tenochtitlán that came to dominate the empire.

Each council would have a kind of "executive council" within it. 4 members would be chosen who would lead, and out of those there would be one tlatcani - the leader of the city. These leaders would not only control the city proper but the surrounding area.


The Huey Tlatcani


In the leading city of Tenochtitlán, the city leaders led the empire. The city council has been compared to the Roman senate. The leader was known as the Huey Tlatcani, or Great Speaker. This was the emperor, who was worshipped as a god. His rule was supported not only by the city council, but also the priests, judges, governors, and a host of other officials. Moctezuma II is the famous Huey Tlatcani who ruled when Hernan Cortes arrived in the New World.

The Huey Tlatcani did have absolute power in a sense. However, he did come to power by a semi-democratic system, and he could be removed from power. How this position was decided upon is not fully understood - it doesn't seem to have been hereditary, but family lines did play some part.






Ancient Aztec Government and
The power of the empire


The ancient Aztec government did not rule an empire in the way we often think of the word. The control didn't stretch into every corner of life - rather, conquered lands were forced to pay tribute, but left a certain amount of freedom. Warriors made small attacks on surrounding peoples and took prisoners which would be sacrificed.
Although the expansion of the empire was often good for the conquered people - better trade and infrastructure, for example, the conquered people still obeyed in fear. Their hatred would cause many of them to turn on the empire when the Spanish gave them the chance.






The Aztec Empire


Most people today are somewhat familiar with the Aztec empire. But it may surprise you to know that there is a great deal of disagreement over what kind of an "empire" it really was. This Aztec empire history may surprise you.

Of course, even the term Aztec is a bit misleading. It's a name that is used for a group of peoples in Central Mexico, but really there wasn't any one people group that was "Aztec". The Mexica people were at the heart of the empire, but there were many other cultures that formed the civilization that the Spanish were to discover.





Estimated area of Aztec power


Aztec empire history





Many years after the Mexica people first built their proud city, Tenochtitlan (later to become Mexico City), they formed an alliance with two other cities - Texcoco (Tetzcoco) and Tlacopan (these three cities are shown as yellow dots in the map above). This Triple Alliance was to rule the Valley of Mexico until the Spanish arrived. However, over time one city become the most powerful - Tenochtitlan. It would become the heart of the Aztec civilization.

Essentially, the history of the empire is a history of city-states. As the empire expanded (which it began to do in earnest around 1428) it conquered more cities. Some cities resisted. Others were conquered and began to pay tribute.


How the empire was ruled


The city of Tenochtitlan was the military power, which spearheaded the conquest of new territory. But the Aztec emperor didn't rule every city state directly. Local governments would remain in place, but would be forced to pay varying amounts of tribute to the Triple Alliance (with most of the tribute going to Tenochtitlan).

For this reason scholar Alexander J. Motyl would call this empire a informalor hegemonic empire.

You also need to remember that the Aztecs didn't necessarily rule connected territories. Because they were conquering cities, they sometimes had power in "pockets" over an area.

But don't think that this was a weak empire. Ruling through a local government ensured that the locals would keep the people happy, and that there would be stability and continuity. This system worked very well for the peoples of the empire.


At its height


The empire might have continued to grow had not the Europeans arrived in 1519. At this time it was at its height, reaching from the Pacific to the Gulf of Mexico, from Central Mexico all the way to Guatemala, El Salvador and Honduras. See this map of the Aztec empire for a visual idea.





Aztec culture


Aztec culture was a rich combination of the cultures of the peoples that made up the Aztec empire, including the Mexicas. Hundreds, even thousands of years of tradition influenced the way people lived in the society. Let's take a look at the different social classes and how they lived...


Social classes in Aztec culture


There were two main social classes in Aztec culture. First, the nobility or pilli, then the common people or macehualli. Each of these was further broken up into groups of people that had quite different lives.


There were also slaves, which were generally well-treated. Slavery was not hereditary - the children of a slave were free. There were ways for a slave to gain freedom, such as purchasing it.

Growing up Aztec


The Mexica people of the Aztec empire had compulsory education for everyone, regardless of gender or class. In the end, people in the Aztec society were generally well educated, though boys received a wider education than girls.


Girls were taught how to run a home, cook, and care for a family, but they were also taught things like crafts and ways to economically run the home. In this way women had a lot of power in society, though it was behind the scenes.

Note: Mandatory education was historically rare in the rest of the world.

Boys learned other trades, and were also taught fighting skills and leadership skills.

Though children started off with similar education, it was eventually split into two main branches. First the calmecac, which was mainly for children of nobles. These children would be educated as priests, teachers, doctors, and leaders of society. Next came the telpochcalli, where children were taught more about Aztec culture and religion, the trades, and skills particular to gender. It seems that there was some freedom to choose a type of education, and perhaps some children were promoted who showed promise in a specific field. It may also be that vocation was chosen based on the religious "sign" children were born under. Just who could go where is a matter of some debate today.

In their mid-teens, adult life would begin. Girls would marry, or stay in the temple and work. Boys might join the military or begin their trade. Marriages were arranged and again strongly tied to religious belief. Some polygamy was practised, though there was still a "primary" wife.


Adult Aztec culture





The noble class had a variety of vocations open to them. They would have positions of leadership and influence, as mentioned above. They would also have some wealth, and unlike the common people they were allowed to enjoy works of art.

The higher level of nobility, usually hereditary to some extent, were the pilli(singular pipiltin). They would hold high positions in government or in the military.

There were also various classes of common people. There were farmers, who were very efficient. There were merchants, who would travel and trade. These people had a fair amount of freedom to be independent and wear stylish clothes. There were artisans of various kinds. Every type of job needed to run a society that you can imagine.

Another occupation of status was to be an athlete. Aztec culture had its own version of Ulama, a game played in Mesoamerica. The game was very popular and the players were celebrities.

Aztec life was permeated by religion. The cycles of the calendar and rituals associated with it to keep nature in balance and appease the gods were a big part of Aztec culture.


Everyday life


Except for the nobility, the people were quite poor, even though great wealth was available in general. The people lived in adobe homes, made of mud bricks. One building was for sleeping and cooking and eating and worship. Another building contained a steam bath. It was believed that the bath was important for good health (a bath is never a bad idea!). Houses of the noble class were bigger, and, as mentioned, were more lavishly decorated.

Life was much as it is most places in the world today - relationships, shopping, music, meals, entertainment was all there. There was poetry, dramatic presentations, art and athletics.

A big part of entertainment for the Aztecs was the Aztec ball game. Special occasions drew the spectators, and the players were celebrities.

But in Aztec culture the warrior was glorified for religious reasons. Taking prisoners and sacrificing them to the gods was an increasingly important ritual. Though life was very structured, it seemed close to chaos as the people tried to avoid natural and imagined disaster.


Age and death


As people got older, and more disease arrived, the the religious healer would be called for. Medical science and religious ritual went side by side. When death came, people would be cremated or buried, depending on how they died and the family's choice.
Aztec Social Classes


The Aztec social classes grew incredibly sophisticated and complex once the Mexica people settled and began to build their empire. It's been said that the class structure was so elaborate that it impressed the Spanish almost as much as the architecture of the empire. And the way it all started is a fascinating story.





The Mexica people, who later became the nucleus of the Aztec empire, were, for a time, a nomadic tribe looking for a home. As they moved south, they came into contact with advanced peoples. Many peoples of the day looked back to the impressive culture of the Toltecs, and the Aztecs came to admire the Toltec heritage. In fact, eventually the word for artistic creations would be toltecat, for the Toltecs, and the Aztecs themselves would claim to be descended from the great Toltec nobles.

The Mexicas were anxious to claim a Toltec heritage, so they chose a nobleman of Toltec origin as their first king, a man named Acamapichtli. He fathered a great many children by 20 wives, and his descendants became the heart of a new social class in the empire - the nobles or pipiltin (singular pilli). From then on, a king would always be chosen from among the pipiltin.

The nobles had many other privileges. They generally received a fuller education, they were allowed to wear fancier clothes and decorate their houses. They were allowed to hold important government offices. But not all had positions of authority - some were craftsmen, or even palace servants. Those who served with distinction could move up the ranks.

Basically, the ruling positions were not hereditary, but preference was given to those in the "royal families".
The Commoners


Technically, there were only two Aztec social classes - the nobles and the commoners. The common people were the macehualtin (singular macehualli). Besides these two main classes, there were a number of different positions that worked like sub-classes. Many of the macehualtin worked the land. They might work a portion of land for life, though technically it was communally owned, and they would work under authority. Some were only hired hands or tenants, and some were even slaves.


Slavery (a slave was a tlacotli) was not hereditary, and there were ways for a slave to gain freedom. If someone was in economic difficulty, they could sell themselves as slaves. Slaves were strictly protected by the law.

As time went by and farming became more efficient, less people were needed to farm, and other parts of society became stronger. Craftsmen and merchants, for example, had a higher social status in society.

Merchants were a privilege class. With the ability to travel and deal in valuable objects, they had a certain amount of freedom many Aztecs didn't have.

Also, in a world where war was so common the soldier had a good chance of rising in the ranks. A soldier who served with distinction could hold an office normally held for a pilli. In this way, almost all levels of government could be shared with the commoner as well as the noble. A warrior who captured many prisoners could be knighted. This would be the first major step up the ranks.


Aztec Society Family


It's very interesting to wonder what life would have been like in a normal Aztec society family. There are many things we do know, although the record is frustratingly sparse. Record keepers were more interested in other aspects of society, and family life was considered the sphere of women.

Still, there are many things we do know. Like other aspects of Aztec culture, life in an Aztec society family was permeated by religious beliefs, right from the start. Each decision was ruled by the laws of religion, and often tied to the sacred days in the Aztec calendar.

The life of a new family began at marriage, typically in the early 20s for a man and mid-teens for the woman. Marriages were arranged by the relatives (though the children may have had input). The parents would have to talk to the religious leaders, and discuss the signs under which both of the children had been born. The wedding day, of course, was chosen for similar religious reasons.


Men and women








All this was full of ceremony and form. In Aztec society family a husband may have had more than one wife - but it would be his primary wife that would go through all the ceremony. The man may have many secondary wives, who would also be officially recognized. The children of the principal wife would be the inheritors - or, in the case of a ruler, only a child from the principal wife would be a successor. Still, the husband was supposed to treat all wives equally in daily life.

As you may imagine, one family could grow very large. As a result, most of the husbands with numerous wives and children were the wealthy ones, with the poor more likely to have one wife.

In one sense, society was dominated by the men. The man was considered the head of the home. However, women had a great deal of power as well. They may have had more power in earlier times, with men taking more power toward the end of the Aztec era.

Women often were able to run business out of their homes, and had a lot of influence in the family and the raising of children. The older widows were much respected, and people listened to their advice.

Adultery was a crime - death was the punishment. Divorce was allowed on certain grounds, presented by the man or woman, property was divided equally and both sides were free.




Marriage and children


Marriage marked the entrance into Aztec adult and independat society. The family was given a piece of land, and they would have their own home. Depending on their situation, both the man and the woman may be involved in working the land. Of course, while a woman was involved in household tasks, a man would be more likely to become a warrior. Though there were many occupations (farmer, priest, doctor, etc), being an Aztec warrior was particularly glorified.

War was even used as a symbol of childbirth. The baby was a "captive" in the womb, struggling to be victorious. The woman, too, was in a battle. In fact, in many ways a woman who died in childbirth was glorified in the same way as a warrior who died in battle, and honoured for her courage.

A child was welcomed into the world and into the religious system. A hymn for the new child to the goddess of child birth went like this:


Down there, where Ayopechcatl lives, the jewel is born, a child has come into the world.
It is down there, in her own place, that the children are born.
Come, come here, new-born child, come here.
Come, come here, jewel-child, come here.


(from the Codex Florentino)



A soothsayer would be called to study the signs of the child. He would inquire about the exact moment of the child's birth. The birth would be cause for more ritual and great celebration.

From what we know, parents loved their children very much. We know that parents often used flowery pet names for their children (for example, a father speaking to his son - "Nopiltze, nocuzque, noquetzale" - sweet son, my jewel, my precious feather.

Then again, when it came to discipline, parents in an Aztec society family ruled with an iron hand.




Work and education





Fathers taking their sons to school



Education, at least in the early years, was the responsibility of the parents. The father would teach the sons, and the mother the daughters. Work and education then would a big part of the Aztec society family. Work could also break up the family - the father might travel, or in the case of warriors may die on the battlefield.

As I mentioned, discipline was often harsh. Up until the age of 8, the preferred method of discipline was simply verbal. But harsh punishments would be in store for the older child, as he was prepared for the harsher realities of Aztec life.

As children grew older, parents would still be in charge of education, but they would more often send the children to school. There were various branches of education that children would be involved in.


Elderly family members


If a family member escaped death on the battlefield or death from illness and so on... they would be among the ueuetque - the wise elders of society. They would offer advice, either informally or on a council. Of course, they were held in high regard in the family itself. The elderly were important in the Aztec society family, and their health care, aging and death was also a matter of ritual and religion.


Summary - Aztec society family


An Aztec society family was ruled in many ways by religion, tradition, and structure. Life was ruled by fate - from beginning to end your family life, occupation, and success depended on the important dates in your life and the structure of the universe and the nature of the gods. At the same time, life was full of celebration, hard work, joy, sorrow, and love, much as it has been in societies around the world for all of history.
Ancient Aztec Religion


Ancient Aztec religion was a complex interaction of gods, dates, directions and colours. It seems that most of the preoccupation in the religion had to do with fear of the nature, and a fear of the end of the world.

By the time the Mexica's Empire (Mexica is the proper name for the tribe at the heart of the Aztec empire) was at its height, the political and religion systems were in close interaction. The actions of the ruling classes and common people can be best understood if we look way back to the Mexica understanding of the creation, or rather creations, of the world. Because the religion was a mixture from various peoples, there are variations. We'll give a general overview here.
In the Beginnings





Quetzalcoatl, the plumed serpent




According to ancient Aztec religion, it took the gods 5 tries to create the world. These attempts were foiled because of infighting among the gods themselves. After he was knocked from his exalted position by rivals, the first creator, Tezcatlipoca, turned into a jaguar and destroyed the world. Under similar circumstances, the world was created and then destroyed with wind, and then two floods.

Each time a creator-god would take a turn being the sun. Finally the gods had a council, and decided one of them would have to sacrifice himself to be the new sun. Nanauatl, a lowly, humble god became the sun, but there was a problem - he wasn't moving. The gods realized that they all must sacrifice themselves so that humans could live. The god Ehecatl sacrificed the others, and a mighty wind arose to move the sun at last.

This was no free sacrifice, however. Not only would the people have to help this weak sun to keep moving, they would also be responsible to repay the sacrifice. The world remained in a precarious position!

Once the sun was dealt with, the world had to be recreated. Quetzalcoatl(meaning feathered serpent) was the one who would create humans. Of course, people had been created several times before, so Quetzalcoatl descended into the underworld to retrieve their bones. He tripped as he fled, and the bones shattered into different sized pieces, which is why people are all different sizes. By adding his own blood to the mix, people came to life.


The calendar and the sun


The ancient Aztec religion was highly focused on keeping nature in balance. One false step could lead to natural disaster. The weak sun could stop moving. In the sky was a constant battle between light and darkness, a battle that would someday be lost.

Huitzilopochtli (Hummingbird of the South) was the warrior sun (either the sun god or the one who fights for the sun god, Tonatiuh (the name given to Nanauatl)). Huitzilopochtli (or Tonatiuh) needed blood sacrifice in order to win the battle against darkness. Either there would be ritual blood-letting, or actual people would be sacrificed. Those sacrificed would rise to fight with him. And so human sacrifices became more and more common in Mexico. Often battles would be fought just to capture prisoners to sacrifice - the Aztec flower war.

Every 52 years, the people were terrified that the world would end. All religious fires were extinguished; people all over the empire would destroy their furniture and precious belongings and go into mourning. When the constellation of the Pleiades appeared, the people would be assured that they were safe for another 52 years.

The world in ancient Aztec religion was divided up into 4 quadrants, and the center - their city Tenochtitlán. The heavens were divided into 13 ascending layers, and the underworld 9 descending layers. The heavens and underworld may be better described as wheels within wheels, a more common form for the Aztecs than layers or lines. The temple in Tenochtitlán was also the place where the forces of heaven and earth intersected.
The end


Prophecies were a part of the ancient Aztec religion. Many scholars today believe that the Aztec people thought that the conquerer Hernan Cortes was their god-hero Quetzalcoatl, who had been banished. Whether or not the more educated upper class shared this belief is questionable.

The afterlife of a person was based mostly on how they died. Some, such as those sacrificed to Huitzilopochtli, would join the battle against the darkness. In ancient Aztec religion, some would eventually be reincarnated as birds or butterflies, or eventually humans. Some would be, for a time, disembodied spirits roaming the earth. Most at some point would have to make the long journey through the 9 levels of the underworld. People would be buried in a squatting position, with items that would help them in their journey. In the end they would live in darkness.










The great temple at Tenochtitlán today,
where temples to the gods Huitzilopochtli and Tlaloc stood
To summarize


Ancient Aztec religion was focused on how the gods, humans and nature were interconnected. There was a strong emphasis on the worship of Huitzilopochtli. The military conquest and ritual sacrifices were all related, and in a great part focused on helping Huitzilopochtli keep the sun strong so that disaster could be averted every 52 years.






Mexico City history


It is believed that central Mexico has been inhabited for thousands of years, but Mexico City history really begins in 1325AD. In recent memory before 1325, the area was actually covered by a lake, Lake Texcoco. But an incredible transformation was about to take place, launching Mexico City history in a way few would have expected.



Mexico City's central square.
This has been the heart of the city since its founding


The founding of Tenochtitlan


The Mexica people were living as outcasts in central Mexico. Legend says they migrated from a place called Aztlan, but they had failed to find a home in this part of Mexico. But they believed that they would see a sign - and eagle perched on a cactus. They saw just such a sign on an island in the middle of Lake Texcoco, and on the 8th of June 1325 their city was born.

It seemed like an unlikely place for a city. Not only was the island small and difficult to access, the lake itself was salty. But the Mexicas knew how to make the best out of a seemingly bad situation. Soon causeways were built leading to the city, making it accessible to merchants and travellers but easy to defend in case of an attack. Aqueducts were built, providing the city with fresh water. A system of agriculture developed, making the area extremely fruitful and efficient, providing the city with food.

As the city was built, roadways grew up and parts of the lake were filled in. Tenochtitlan was to become the "Venice of the New World", a series of canals, city and farmland, well planned, equal or better than any city in the world.


The Aztec Empire


In this early Mexico City history, Tenochtitlan immediately became the centre of a growing empire. The Mexicas developed alliances with other cities, got tribute from other peoples, and ruled throughout central Mexico. The city became a major centre for trade, military operations, culture, and political power.


The Spanish arrive


Hernan Cortes from Spain arrived with his army in 1519, and in two years after a 79 day siege had captured Tenochtitan. The old Aztec city was mostly destroyed, and was rebuilt by 1525. It should be noted, however, that this was not simply a brand new city. Much of the Aztec culture and layout, and of course many of the people, remained the same. To understand Mexico City history, it's important to remember that it's not so easy to wipe out an empire. Just as the Aztec way of life had grown from the many cultures before it, so the new Mexico City, even the one we know today, is still in part the ancient city of Tenochtitlan.

Mexico City was still the centre of culture and power in Mexico. It was also where places as far as Cuba, Florida and even the Philippines were administered. No doubt Cortes had recognized the importance of the city, and continued its tradition of power.








The Fall of the Aztec Empire


What caused the fall of the Aztec empire? We do know that there were a number of factors involved, not just one. There are probably many factors that we don't know about that were already contributing to the weakness of the empire. But let's look at some of the most obvious, immediate factors:
The sacrifices





Armour of a Spanish solder
On display at the
National Anthropological Museum, Mexico City



There's little doubt that the ritual Aztec sacrifice contributed to the fall of the Aztec Empire, and in more ways than one. First, killing thousands of people, whether you or your neighbours, simply can't be good for a society. The loss of people in a loss that can't be calculated. Who knows how it would have been different if these people and their children had swelled the ranks that fought the Spanish, not to mention the other contributions they would have made.

And although the Aztecs certainly weren't the first people ever to sacrifice humans, the fact that they did and the incredible number they sacrificed led to the hatred of some of the surrounding peoples. The powerful city-state of Tlaxcala was one of these. Many of their own had been sacrificed, and in the end they joined the Spaniards to fight the Aztecs. It may be that the Spanish simply were an excuse to start what was already an inevitable civil war.

Lastly, it's believed that the horror of human sacrifice highly motivated the Spaniards to conquer what they considered an evil culture - in other words, they used it to justify their war with the empire.
Religion


Naturally, religion played a part because of the sacrifices. It has been commonly believed that, at first, the Aztecs thought that the Spanish were gods.

This belief is more and more being questioned - it may be a fabrication. Religious, yes, but the nobles were also well educated. Even if they did have such a passing thought, it's unlikely it lasted long. In addition, there's no reason to believe that Cortes and his men wouldn't have been welcomed anyway, with similar results. Modern scholars are questioning whether this belief in the return of the god Quetzalcoatl was real or a later rewrite of history.

Even more interesting is the theory that, at one point, the Aztecs did not completely destroy the Spanish army because they wanted more people to sacrifice to their gods. This was a tactical error that at least hastened the fall of the Aztec empire.
Disease


Disease played a huge part in the fall of the Aztec empire. Here's what happened.


After Cortes landed in Mexico, another Spanish army came from Cuba to make sure he followed orders. Cortes would have none of that, and went to fight them. In this new group was an African being held as a slave, who had smallpox, a very contagious disease.

One of Cortes' men contracted the disease. When they returned, the Aztec army quickly overwhelmed the Spanish, killing many and causing the rest to retreat. The soldier was killed, and, likely when his body was looted, an Aztec caught the disease.

Quickly, smallpox spread among the population. The people had no resistance and no idea how to treat it. In many cases, everyone in a house died. With no time to bury so many people, houses were simply demolished over the bodies. It is estimated that 5-8 million died.

During the siege of Tenochtitlán in 1520, the population was not only low on food but dying of smallpox. 25% of the empire is said to have been lost to the disease alone. But more importantly, the Aztec chain of command was in ruins. The emperor, Cuitláhuac, died of smallpox, along with many of the leaders of the army.


(Actually, there were a series of epidemics over the next 50-60 years, which killed far more than the first epidemic. Called by the Aztecs cocoliztli, much of the death toll may have been caused by salmonella enterica)
Tactics


The tactics of the Spanish army certainly played a role. The Mexicas were simply used to playing by different rules. However, the Aztecs soon got wise to the ways that the Europeans fought, and this almost led to their victory. But Cortes still used clever tactics in the final siege that, in combination with his native allies and the epidemics of disease, brought about the fall of the Aztec empire.
Summary of the
Fall of the Aztec Empire


Here's a (very) brief summary of the fall of the Aztec empire, after the arrival of Hernando Cortes until the fall of Tenochtitlán.


 1519 (March 4): The Spaniards land in what is now Veracruz. The natives greet him with gifts. A contingent from Tenochtitlán also arrives with gifts. Cortes showed force and demonstrated his canons, terrifying the messengers.


 Cortes sinks all the ships except one small vessel, and moves to the city-state of Tlaxcala. Generally speaking they begin on friendly terms.


 The Spanish went on to Cholula. It's unclear what happened, but in the end many people in the city were killed by the Spanish.


 1519 (Nov 8): Cortes and army arrives at Tenochtitlán, and begin on good terms. However, Cortes takes charge and demands tribute and some Roman Catholic shrines to replace the Aztec gods.


 Cortes returns to the coast to defeat a rival Spanish army. The remaining soldiers join him.


 The Aztecs revolt, driving the Spanish from the city. Cuitláhuac becomes emperor.


 The Spanish go to Tlaxcala and make an alliance with them.


 Most Aztec cities are conquered, and a siege of Tenochtitlán begins.


 1521 (13 August): The last Aztec emperor, Cuauhtémoc, surrenders to Cortes.