The Aztec Empire was a shifting and fragile alliance of three principal city-states. The largest and most powerful among the three was Tenochtitlán, the island city built by the Mexica people, also known as the Aztecs. The Aztec Triple Alliance exerted tremendous power over a wide swath of central Mexico for just shy of 100 years (1420s to 1521) before falling to Spanish conquistadors led by Hernán Cortés.

According to Aztec mythology, the ancient people who settled Tenochtitlán came from a legendary land called Aztlán (hence the later adoption of the name Azteca or Aztecs). Modern scholars of Mesoamerica now believe that the Mexica people who built Tenochtitlán were the last in a long migration from the parched American Southwest to the fertile Valley of Mexico, the site of modern-day Mexico City.

By the time the Mexica arrived in the early 1300s, there were already 40 to 50 established city-states (called altepetl in the Nahuatl language) in the valley, most of them ringing the great Lake Texcoco. The most dominant altepetl at the time was Azcapotzalco, to which the Mexica newcomers paid tribute and labored as mercenaries. The poor and powerless Mexica built their settlement on an island in the middle of Lake Texcoco.

“They got that spot because nobody else wanted it,” says Camilla Townsend, a historian at Rutgers University and author of Fifth Sun: A New History of the Aztecs. “It wasn’t good for farming the corn, beans and squash that they all lived on.”

Soon, however, the Mexica learned an agricultural trick from the neighboring Xochimilca, who taught them to build productive raised bed gardens in the shallows using basket-like fences of woven reeds. In time, the previously unattractive island location transformed into a central trading hub with canoes filled with goods crisscrossing the lake to buy and sell in Tenochtitlán.

While settlers around Lake Texcoco thrived agriculturally, they lived under volatile rulership. Power dynamics in 14th-century Mexico were complicated to say the least.

“Every city-state was always on the edge of civil war,” says Townsend, the result of an energetically polygamous ruling class.

Kings, known as tlàtoani (meaning “speaker” or “mouthpiece”), took multiple wives as gifts and tributes from their political allies. The polygamous unions yielded dozens of potential heirs, each vying for the throne with the military backing of their mother’s home city.

In 1426, the tlàtoani of Azcapotzalco, still the most powerful city state, died suddenly. His heirs, each representing the interests of another city-state, began killing each other off in a desperate grab for the throne. Chaos ensued.

The tlàtoani of Tenochtitlán at the time was a man named Itzoatl or “Obsidian Snake.” Itzcoatl himself was an unlikely heir to the Tenochtitlán throne, as the son of a former king and an enslaved woman. But he was a savvy schemer and knew an opportunity when he saw it.

Itzcoatl sought allies from towns that had been wronged by Azcapotzalco. But not only that, he looked for bands of brothers from second-and third-tier queens who had little chance of rising to power on their own. That’s how Itzcoatl forged an alliance between Tenochtitlán and aspiring families in the two smaller city states of Tlacopan and Texcoco.

Together, this unlikely coalition of the least-powerful bands of brothers waged war against chaotic Azcapotzalco and seized power in a coordinated coup. The Triple Alliance was born.

Once Azcapotzalco was subdued, the Triple Alliance combined its armies to intimidate city-states and villages across the Valley of Mexico and beyond. Unlike the Roman Empire, which imposed Roman culture, language and government on dominated states, the Triple Alliance took an ad hoc approach to its rule.

“[The Triple Alliance] was an organized, but still informal and shiftable set of arrangements,” says Townsend. “Some conquered city-states could continue in power unmolested as long as they gave tribute. Others that had been more 'difficult'—perhaps had fought very hard or had killed emissaries—were destroyed.”

The Huastec people, for example, fought fiercely against the invading armies and paid a steep price for their insolence. According to a Spanish friar writing a century later, “[The allied soldiers] killed old and young, boys and girls, annihilating without mercy everyone they could, with great cruelty and with the determination to remove all traces of the Huastec people from the earth.”

Loot and tribute in the form of women, warriors, food, textiles and precious materials was shared among Tenochtitlán, Tlacopan and Texcoco, but Tenochtitlán was clearly the “senior partner,” says Townsend, due to its size and the fact that Itzcoatl came up with the alliance idea in the first place.

Because of its now-prized location on the lake, Tenochtitlán grew into a bustling market town rich with the spoils of conquest and populated by skilled artisans catering to a growing noble class.

Townsend says that every ancient culture practiced some form of human sacrifice and that was almost certainly true of indigenous people in the Americas, not just the Aztecs. In the world of 14th- and 15th-century Mexico, prisoners of war were routinely sacrificed as both a tribute to the conquering gods and a warning to upstart city-states.

Before they rose to power as part of the Triple Alliance, the Aztecs didn’t perform large-scale human sacrifices. But Townsend says that something shifted in the 1470s and 1480s when Tenochtitlán grew to be the dominant force in all of central Mexico.

“[Tenochtitlán] was the king of the mountain and they needed to maintain that position,” says Townsend. “The longer you’ve been in charge and the longer you’ve been demanding tributes from others, the worse it’s going to be if you’re ever brought down.”

A decision was made to use terror as a weapon for keeping rebellious city-states in line. Soon the Aztecs were not only sacrificing a handful of prisoners of war to satisfy their gods but demanding tributes of hundreds or even thousands of young people to stand before the cutting stone.

According to one Nahuatl record, soldiers would kidnap people from territories that the Alliance was interested in conquering and bring them to the Templo Mayor (Great Temple) in Tenochtitlán to witness one of these mass human sacrifices. Then they’d send the captives home to spread word of what they had seen.

Not everyone was in favor of the sacrifices, says Townsend, who points to Aztec songs and poems decrying the violence and bloodshed. But the ruling and noble classes of Tenochtitlán saw no other way to maintain their precarious rule and fuel their opulent lifestyles.

“There are periods in every nation’s history where they do dastardly things to maintain power, and that’s certainly something the Aztecs did,” says Townsend.

In her book, Townsend upends many of the myths of the Spanish Conquest, namely that the indigenous enemies of the Aztecs immediately flocked to the side of the foreign invaders in order to crush their hated rival. And that the Aztecs who weren’t killed by the sword were finished off by epidemic European diseases like smallpox.

Those conventional explanations are belied by historical texts written by the Aztecs themselves. Soon after the conquest, Spanish friars taught the Roman alphabet to young Aztec noblemen so they could read the Bible. Some of those same young men collected centuries of Aztec history from family members and traditional storytellers and wrote them down in phonetic Nahuatl.

Townsend pored through dozens of these Nahuatl annals to piece together a fresh perspective on Aztec history, including the portentous arrival of Cortés and the fall of the empire.

What’s clear now is that the Tlaxcalans, longtime rivals of the Aztecs who never succumbed to the Triple Alliance, didn’t immediately throw their lot in with the Spanish. The Tlaxcalans battled the Spanish forces for a week before deciding, like so many other indigenous Americans, that they simply couldn’t compete with the invaders’ superior technology.

“The more the Indians got to know the Europeans—and the more they saw the ships, the compasses, the canons, etc.—the more they realized that they’re going to lose this war eventually,” says Townsend.

Even after Montezuma’s death in 1520, the Aztecs fought the Spanish for another year. But once the Tlaxcalans and other indigenous groups joined the Spanish, the Aztecs’ fate was sealed. Tenochtitlán was razed to the ground and countless Aztecs died from European diseases, but that wasn’t the end of the story.

Those Aztecs who survived the fall of Tenochtitlán were forced to make peace with the new reality of colonial rule. Like the authors of the Nahuatl history, they bent to the will of their Spanish overlords while retaining the language and stories that tied them to their once-rich culture.

“The Aztecs were conquered,” writes Townsend in Fifth Sun, “but they also saved themselves.”