When the Spanish conquistadorsSpanish soldiers who traveled to the Americas to conquer indigenous peoples and claim land for Spain. arrived in the Valley of Mexico in 1519 CE, they encountered the Aztec Empire, which was the strongest and most dominant Mesoamerican civilization of the time. The Aztec expanded their empire across the region due primarily to military strength, strategic alliancesAgreements between groups or societies to work together toward a shared goal. and the tributeGoods, wealth, or people that a conquered group is forced to give to the ruling power. system.
FactsthatCrunchHow Did the Aztec Control the Peoples They Conquered?
The Aztec controlled conquered groups mainly through a tribute system that required defeated societies to hand over goods and supply people for ritual sacrifice. This arrangement let the Aztec rule a wide territory without placing large armies in every region. Conquered peoples kept their local leaders but had to meet these demands or face military punishment.
Early Aztec History
Following the Aztec’s founding and construction of Tenochtitlan in the Valley of Mexico in 1325, they quickly established their authority across the other societies in the valley. This period was the early history of the Aztec Empire. At the time the Valley of Mexico was populated by many different powerful civilizations, including: Chalco, Tepanec, Tlacopan, Texcoco, Culhuacan, and Chichimec. Several of these civilizations were also on the shores of Lake Texcoco, including the Culhuacan which was on the south shore.
One of the ways in which the Aztec expanded in strength and wealth at the time was by acting as mercenariesFighters who work for another group or country in exchange for pay or rewards. and warriors for other societies in the region. For example, in the decades after the founding of Tenochtitlan they worked as warriors for the Tepanec people. The Tepanec used the Aztec to help with their battles and campaigns in the region against other rival societies. For their help the Aztec received portions of the wealth that the Tepanec gathered from the societies that they defeated. As a result, the city of Tenochtitlan grew in importance and wealth throughout the 14th and 15th centuries. In general though, the Aztec were subjects of the more powerful Tepanec and Aztec leaders were only allowed to remain in power by paying tribute to the Tepanec. Also, during this time period, Aztec rulers increased the power of their society by forming strong alliances with other societies around Lake Texcoco. However, the relationship between the Aztecs and the Tepanec soon became strained and a conflict emerged.
FactsthatCrunchHow did the Aztec go from hired fighters to rulers of the Valley of Mexico under the Tepanec?
Aztec Triple Alliance
Itzcoatl became the leader of the Aztec in 1427 and became the fourth tlatoaniThe Aztec word for ruler or leader of the Aztec people. of the Aztec people. He reigned over the Aztec Empire from 1427 until 1440, and is best remembered as the leader who saw the Aztecs become the most powerful Mesoamerican society in the Valley of Mexico. For example, as leader he famously formed an alliance with two other societies in the area in order to overthrow their mutual rivals. The Aztecs, Texcoco and Tlacopan joined forces in 1428 to create the Triple Alliance. Together they fought against the Tepanec and challenged them for superiority in the Valley of Mexico. Over time the three were able to overpower all other societies in the Valley of Mexico. As well, the Aztec became the strongest of the Triple AllianceA union of three city-states, the Aztec, Texcoco, and Tlacopan, formed in 1428 to defeat rival powers. and Tenochtitlan became the center of power in the region.
FactsthatCrunchExpansion of the Aztec Empire
All of the Aztec rulers at this time pushed forward with expanding the Aztec Empire across Mexico and strengthening the power of Tenochtitlan. In fact, the city grew in size and importance during this time as the Aztec culture came to dominate the region. For example, by the early 16th century, Tenochtitlan is estimated to have been three to five square miles (eight to thirteen square kilometers), and have a population of between 200,000 and 300,000 people. This means that it was one of the largest cities in the world at the time and larger than any city in Spain. As well, the Aztec Empire had spread far from the Valley of Mexico during this time and, at its height, the empire consisted of land across most of central Mexico including the coastlines in both the Gulf of Mexico and Pacific Ocean. This vast expansion meant that the Aztec had conquered and suppressed many different groups of Mesoamerican peoples. The Aztec controlled these different societies by forcing them to provide tributes for payment and ritual sacrificeThe killing of people or animals as an offering to gods, required from conquered Aztec subjects..
By the time of the arrival of Spanish conquistadors to the Aztec territory in 1519, the Aztecs were the most powerful society in all of Mesoamerica.
FactsthatCrunchBy the early 1500s, Tenochtitlan may have held 200,000 to 300,000 people, making it one of the largest cities in the world and bigger than any city in Spain.
The city was built on an island in Lake Texcoco. Raised roads called causeways linked it to the mainland, and tribute from conquered peoples across central Mexico flowed into its markets and temples.
Explore Aztec Empire · 1325 – 1521 CE
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Key Vocabulary
Conquistadors
Mercenaries
Tribute
Tlatoani
Triple Alliance
Alliances
Ritual sacrifice
Frequently Asked Questions
How did the Aztec Empire expand?
The Aztec Empire grew through military strength, strategic alliances, and a tribute system. They conquered rival societies and forced them to pay goods and provide people for sacrifice. Alliances with nearby city-states also helped them defeat stronger enemies and gain wealth.
What was the Aztec Triple Alliance?
The Triple Alliance was a union formed in 1428 CE between the Aztec, Texcoco, and Tlacopan. These three city-states joined forces to overthrow the powerful Tepanec in the Valley of Mexico. Over time the Aztec became the strongest member, and Tenochtitlan became the center of power.
Who was Itzcoatl?
Itzcoatl was the fourth tlatoani, or ruler, of the Aztec people, reigning from 1427 to 1440 CE. He is best remembered for leading the Aztec to become the most powerful society in the Valley of Mexico. Under his rule, the Aztec formed the Triple Alliance and defeated the Tepanec.
How large was Tenochtitlan at its height?
By the early 16th century, Tenochtitlan covered about three to five square miles (8 to 13 square kilometers). Its population was between 200,000 and 300,000 people. This made it one of the largest cities in the world and bigger than any city in Spain at the time.
How did the Aztec control the people they conquered?
The Aztec controlled conquered groups mainly through a tribute system. Defeated societies had to provide goods as payment and supply people for ritual sacrifice. This system let the Aztec rule a wide area without stationing large armies everywhere.
When did the Spanish arrive in the Aztec Empire?
Spanish conquistadors arrived in the Valley of Mexico in 1519 CE. At that point, the Aztec were the most powerful society in all of Mesoamerica. Their empire stretched across most of central Mexico, reaching both the Gulf of Mexico and the Pacific Ocean.
Cite This Article
To cite this article as a source, use one of the formats below.
MLA: Beck, Elias. “How Did the Aztec Empire Expand?: A Detailed Summary.” HistoryCrunch, 26 October 2026, https://historycrunch.com/how-did-the-aztec-empire-expand/.
APA: Beck, E. (2026). How Did the Aztec Empire Expand?: A Detailed Summary. HistoryCrunch. https://historycrunch.com/how-did-the-aztec-empire-expand/
Chicago: Beck, Elias. “How Did the Aztec Empire Expand?: A Detailed Summary.” HistoryCrunch. October 26, 2026. https://historycrunch.com/how-did-the-aztec-empire-expand/
Sources
- The Met (Heilbrunn Timeline): Aztec art
- Fordham Internet History Sourcebooks
- Richard Townsend, The Aztecs.
- Michael E. Smith, The Aztecs.
