Between 1519 and 1521, Spanish conquistadors, led by Hernán Cortés, overthrew the Aztec Empire. This event is called the Spanish conquest of the Aztec Empire. Cortés helped old enemies of the Aztecs defeat them in one of the most important events in the Spanish colonization of the Americas.

The Spanish conquest was devastating to the Aztec people.  By 1680, 94% of the Aztec population had died.

End of the Empire

In 1515, two of the states in the Aztec Empire rebelled.  This was nothing new for the Aztecs.  However, this time, the Tlaxcala and Huexotzingo rebels beat the Aztec military.

Then, in April 1519, Spanish conquistadors, led by Cortés, arrived on the coast of Mexico. In August they marched to Tenochtitlan, the capital of the Aztec Empire. At first, Montezuma II, the Aztecs' ruler, invited the Spanish into Tenochtitlan, and things were friendly.  Even when the Spanish made Montezuma II a prisoner, the Aztecs stayed friendly.

However, soon, while Cortés was away, Spanish soldiers attacked and killed many Aztecs during a festival.  When Cortés got back, he got Montezuma II to tell the Aztecs to stop fighting the conquistadors. By this time, though, the Aztecs had made Montezuma II's brother, Cuauthemoc, the king. Nobody did what Montezuma II said. They kept fighting the conquistadors, and they killed two out of every three Spanish soldiers. In July 1520 the Spanish survivors fled to Tlaxcala, where enemies of the Aztecs protected them.

Ten months later, Cortés came back to Tenochtitlan with more Spanish soldiers but mostly Tlaxcaltecas and other indigenous enemies of the Aztecs. They started a siege of Tenochtitlan, so that no food or supplies could get in.  After 91 days, without any food, and with disease throughout the city, Cuauhtemoc finally surrendered to the Spanish on August 13, 1521.  The Spanish destroyed Tenochtitlan.  They started a Spanish colony that they named New Spain.  The Aztec Empire had ended.

Weapons
There were many different reasons why the Spanish were able to take over the Aztec Empire.
Different wepons were used through the battle to help Cortes overrule the aztecs.
First, their weapons and armor were better than the Aztecs'.  Aztec warriors had only cotton armour and shields made of wood or reeds to protect them.  The Spanish had metal armor and shields.

For weapons, Aztec warriors had a few choices:
 Macuahuitl: A very sharp sword, with a point made of obsidian, which can be sharpened like glass.  This sword could also be used as a club
 Atlatl: A weapon used to throw spears or darts 
 Bows and arrows

None of these weapons could compare to the conquistadors' guns and steel swords.  Their horses and war dogs gave them even more of an advantage against the Aztecs.

Religion

As early as 1528, reports have said that Montezuma II thought Hernán Cortés was the Aztec god Quetzalcoatl.  Aztec legends said that Quetzalcoatl would return as a man, and Cortés had arrived on Quetzalcoatl's birthday.  Aztec writings from the time say that when Montezuma II greeted Cortés, he gave an abdication speech, giving up the Aztec throne to "Quetzalcoatl-Cortés":

As historian David Carrasco explains: Motecuhzoma II is welcoming "Quetzalcoatl-Cortes ... back to his city in order to reoccupy the throne which has been guarded by Montezuma and the other [kings] ... The ancient prophecy has been fulfilled and the returning lord is invited to occupy his throne and visit the palace.  There could hardly be a clearer statement of returning the sovereignty to the original king."

Other causes
Some historians say that the Spanish conquistadors were not the only reason the Aztec Empire fell apart.  By 1519, the Empire had other problems that made it easier for Spain to take it over.  For example:
 More and more, nobles were being allowed to marry commoners.  Their children automatically became nobles.  This meant there were too many nobles and not enough commoners to do the everyday work in the Empire.  Since the commoners were the ones that grew the food for the Empire, this meant there was not enough food for everyone.
 The Aztec government had started to use terror to keep control over the states it had taken over.  When the Spanish conquistadors got to Tenochtitlan, they said the Aztecs often held public ceremonies.  They would invite the leaders of the states they took over to come. Then they would do many human sacrifices. The conquistadors said that the Empire sacrificed 20,000 people every year  an average of 55 people a day.
 The Aztec government was making the states they took over  and regular people in Tenochtitlan  pay more and more money in tributes (which were like taxes).
 When Cortés and his conquistadors came to Tenochtitlan, they brought smallpox. This very contagious disease killed a huge number of Aztecs.
Cortes wanted to conquer the aztecs for gold glory and god. 
Because of these things, many people in the Aztec Empire  were unhappy.  Some of them helped the Spanish conquistadors take over the Empire.  Some historians, like Brian Fagan and Nadia Durrani, say that the Empire would have fallen apart even if the Spanish had never come.  However, because so many people had died of smallpox, there were also not enough people left to fight against the conquistadors when they did come.

After the Empire
Under Spanish control, the Aztec Empire did not exist any more.  The Spanish tried to change the Aztecs into Catholics and make them act like Spanish people.  They made it easier to change from Aztec rule to Spanish rule by letting many Aztec nobles become Spanish nobles.

The conquistadors rewarded people who had helped them defeat the Aztecs.  Many received an Encomienda, a village full of Aztecs who were forced to work for them.  This was not much different from what many serfs had done during the Aztec Empire.  However, workers were badly abused, and many died.  Because of this, a Spanish bishop named Bartolomé de las Casas suggested using African slaves to work in New Spain instead.  Later, when he saw how much worse African slaves were treated, las Casas changed his mind about this.

By 1680, 94% of the Aztec population had died.  This happened for a few reasons:
 Disease, especially smallpox, which the conquistadors had brought from Europe
 Being forced to work too hard with too little food, which caused malnutrition
 Famine (not being able to grow enough food for themselves, because they were being forced to grow food for other people)
 Abuse from the people who were forcing them to work

After taking over the Aztec Empire, the Spanish conquistadors moved on to take over other parts of Mesoamerica.  During the same 160 years  from 1520 to 1680  between 85% and 95% of Mesoamerica's native population died.

Related pages 
 Aztec
 Aztec Empire
 Spanish Empire
 Conquistadors

References

Aztec
Colonialism
16th century in Spain
History of North America