Most ethnic groups of central Mexico in the post-classic period shared basic cultural traits of Mesoamerica, and so many of the traits that characterize Aztec culture cannot be said to be exclusive to the Aztecs. For the same reason, the notion of "Aztec civilization" is best understood as a particular horizon of a general Mesoamerican civilization. The culture of central Mexico includes maize cultivation, the social division between nobility (pipiltin) and commoners (macehualtin), a pantheon (featuring Tezcatlipoca, Tlaloc, and Quetzalcoatl), and the calendric system of a xiuhpohualli of 365 days intercalated with a tonalpohualli of 260 days. Particular to the Mexica of Tenochtitlan was the patron God Huitzilopochtli, twin pyramids, and the ceramic ware known as Aztec I to IV.

From the 13th century, the Valley of Mexico was the heart of dense population and the rise of city-states. The Mexica were late-comers to the Valley of Mexico, and founded the city-state of Tenochtitlan on unpromising islets in Lake Texcoco, later becoming the dominant power of the Aztec Triple Alliance or Aztec Empire. It was an empire that expanded its political hegemony far beyond the Valley of Mexico, conquering other city states throughout Mesoamerica in the late post-classic period.

Aztec culture and history is primarily known through archaeological evidence found in excavations such as that of the renowned Templo Mayor in Mexico City; from indigenous writings; from eyewitness accounts by Spanish conquistadors such as Cortés and Bernal Díaz del Castillo; and especially from 16th- and 17th-century descriptions of Aztec culture and history written by Spanish clergymen and literate Aztecs in the Spanish or Nahuatl language, such as the famous illustrated, bilingual (Spanish and Nahuatl), twelve-volume Florentine Codex created by the Franciscan friar Bernardino de Sahagún, in collaboration with indigenous Aztec informants. Important for knowledge of post-conquest Nahuas was the training of indigenous scribes to write alphabetic texts in Nahuatl, mainly for local purposes under Spanish colonial rule. At its height, Aztec culture had rich and complex philosophical, mythological, and religious traditions, as well as achieving remarkable architectural and artistic accomplishments.

In the Valley of Mexico (c. 1250 CE), there existed numerous city-states, including Chalco, Xochimilco, Tlacopan, Culhuacan, and Azcapotzalco. The most powerful were Culhuacan on the south shore of Lake Texcoco and Azcapotzalco on the west shore. As a result, when the Mexica arrived in the Valley of Mexico as a semi-nomadic tribe, they found most of the area already occupied. In roughly 1248, they first settled on Chapultepec, a hill on the west shore of Lake Texcoco, the site of numerous springs.

In time, the Tepanecs of Azcapotzalco ousted the Mexica from Chapultepec and the ruler of Barbara, Cocoxtli, gave the Mexica permission to settle in the empty barrens of Tizaapan in 1299. There they married and assimilated into Culhuacan culture.

In 1323, they asked the new ruler of Culhuacan, Achicometl, for his daughter, in order to make her the goddess Yaocihuatl. Unknown to the king, the Mexica actually planned to sacrifice her. The Mexican believed that by doing this the princess would join the gods as a deity. As the story goes, during a festival dinner, a priest came out wearing her flayed skin as part of the ritual. Upon seeing this, the king and the people of Culhuacan were horrified and expelled the Mexica.

Forced to flee, in 1325 they went to a small island on the west side of Lake Texcoco where they began to build their city Tenochtitlan, eventually creating a large artificial island. It is said that the Aztec god, Huitzilopochtli, instructed the Aztecs to found their city at the location where they saw an eagle, on a cactus, with a snake in its talons (which is on the current Mexican flag). The Aztecs, apparently, saw this vision on the small island where Tenochtitlan was founded.

In 1376 the Mexica elected their first tlatoani(can be translated into English as 'king'), Acamapichtli, following customs learned from the Culhuacan. These customs required cleaning daily nonstop as a ritual.

Huitzilíhuitl, a good politician, continued the policies of his father, seeking alliances with his neighbors. He founded the Royal Council or Tlatocan and established four permanent electors to advise the new king, in his inexperience, at the beginning of each reign. Huitzilihuitl as depicted in the Tovar Codex. He married Ayauhcihuatl, daughter of Tezozómoc, the powerful tlatoani of Azcapotzalco, and obtained a reduction of tribute payments to the symbolic level. Their son Chimalpopoca would succeed his father as tlatoani. After the death of Ayaucíhuatl, Huitzilíhuitl married a second time, to Miahuaxihuitl. She bore him Moctezuma I, who also succeeded to the throne as the fifth Huey Tlatoani of Aztecs. During his reign, the weaving industry grew. It provided cotton cloth not only for Tenochtitlan, but also for Azcapotzalco and Cuauhnāhuac. The Mexicas no longer had to dress in coarse ayates" of maguey fibers, but were able to change to soft, dyed cotton.

On the day of Chimalpopoca's coronation in 1417 (some sources say 1416 or 1418), his brother Tlacaelel I was named high priest. From this point on the ecclesiastical and governmental offices among the Aztecs were separate. When he assumed the throne at age 20, Tenochtitlan was a tributary of the Tepanec city of Azcapotzalco, which was ruled by his grandfather Tezozomoc. This alliance, and the Mexicas' position within it, was strengthened by Tenochtitlan's loyalty during Tezozomoc's 1418 war with Ixtlilxochitl I of Texcoco. The conquered city was granted to Tenochtitlan as a tributary. Chimalpopoca also had a causeway constructed to Tlacopan. The causeway contained openings spanned by wooden bridges, which were removed at night. Also during his reign he dedicated a stone for sacrifices in the Tlacocomoco section of Tenochtitlan. To him is attributed the conquest of Tequizquiac.

The death of Tezozomoc in 1426 brought his sons Tayatzin and Maxtla to the throne, with Maxtla most likely poisoning Tayatzin. In 1428, Maxtla was overthrown by the nascent Aztec Triple Alliance, which included the Mexicas of Tenochtitlan and the Acolhua of Texcoco, as well as Maxtla's fellow Tepanecs of Tlacopan. With the rise of the Aztec empire, Tlacopan became the predominant Tepanec city, although both Tenochtitlan and Texcoco eclipsed Tlacopan in size and prestige.

Itzcoatl was the natural son of tlàtoāni Acamapichtli and an unknown Tepanec woman from Azcapotzalco. He was elected as the king when his predecessor, his nephew Chimalpopoca, was killed by Maxtla of the nearby Tepanec āltepētl (city-state) of Azcapotzalco. Allying with Nezahualcoyotl of Texcoco, Itzcoatl went on to defeat Maxtla and end the Tepanec domination of central Mexico. After this victory, Itzcoatl, Nezahualcoyotl, and Totoquilhuaztli, king of Tlacopan, forged what would become known as the Aztec Triple Alliance, forming the basis of the eventual Aztec Empire.

The Triple Alliance was formed from the victorious factions of a civil war fought between the city of Azcapotzalco and its former tributary provinces. Despite the initial conception of the empire as an alliance of three self-governed city-states, Tenochtitlan quickly became dominant militarily. By the time the Spanish arrived in 1519, the lands of the Alliance were effectively ruled from Tenochtitlan, while the other partners in the alliance had taken subsidiary roles. It was an alliance of three Nahua altepetl city-states: Mexico-Tenochtitlan, Tetzcoco, and Tlacopan. These three city-states ruled the area in and around the Valley of Mexico from 1428

The first Tlatoani of the Triple Alliance was Itzcoatl and he, along with his Texcocan co-ruler Nezahualcoyotl, began expanding the territory dominated by the alliance towards the south, conquering Nahua-speaking cities like Cuauhnahuac (now Cuernavaca), and towards Huexotla, Coatlinchan, and Tepoztlan in the modern-day state of Morelos which was then dominated by the Tlahuica. During this period the Nahuan cities immediately on the lakeside, such as Xochimilco, Culhuacan and Mixquic were also subdued.

During a disputed Tepanec succession, Maxtla killed his brother and usurped the throne then laid siege to Tenochtitlan. An alliance of opponents under Nezahualcoyotl drove Maxtla back to siege at Azcapotzalco, which fell after 114 days, and the tyrant was executed. Tenochtitlan, Texcoco and Tacuba then created the Triple Alliance, which became the foundation of the powerful Aztec Empire.

Two of the primary architects of the Aztec empire were the half-brothers Tlacaelel and Moctezuma I. Moctezuma I began the expansion in earnest. First he had to reconquer towns which were first conquered by Itzcoatl, but had since rebelled. He asked a number of smaller cities to contribute to the construction of a new Great Temple, and only Chalco refused, which caused Moctezuma to start a war against them which lasted for several years. He then conquered Huastec territory under a pretext of securing Aztec merchants in that area, and then he went to war against the Mixtecs of Coixtlahuaca. Later Moctezuma marched upon the Totonacan cities of Vera Cruz and conquered Xalapa, Cosamaloapan, Cotaxtla (modern day Cuetlachtlan), Ahuilizapan (Modern day Orizaba) and north into Huastec territory conquering Tuxpan and Xilotepec. Tlacaelel recast or strengthened the concept of the Aztecs as a chosen people and elevated the tribal god/hero Huitzilopochtli to the top of the pantheon of gods. In tandem with this, Tlacaelel increased the level and prevalence of human sacrifice, particularly during a period of natural disasters that started in 1446 (according to Durán). At the start of Tlacaelel's tenure, the Mexica were vassals. By the end, they had become the Aztecs, rulers of a socially stratified and expansionistic empire.

In 1452 There was a flood in the Aztec’s great city Tenochtitlán. This damaged the city and caused a great famine and starvation. It is estimated that over 10,000 people were sacrificed to the gods during this time to make the famine stop. Much time and many resources were spent on restoring the great city and building a temple in the gods’ honor so that they could regain favor with them.

During the reign of Moctezuma I, the "levee of Nezahualcoyotl" was constructed, reputedly designed by Nezahualcoyotl. Estimated to be 12 to 16 km (7.5 to 9.9 mi) in length, the levee was completed circa 1453. The levee kept fresh spring-fed water in the waters around Tenochtitlan and kept the brackish waters beyond the dike, to the east.

During his youth, his military prowess gained him the favor influential figures such as Nezahualcoyotl and Tlacaelel I, and thus, upon the death of Moctezuma I in 1469, he was chosen to ascend to the throne, much to the displeasure of his two older brothers, Tizoc and Ahuitzotl. It is also important that the Great Sun Stone, also known as the Aztec Calendar, was carved under his leadership. In the Year 1475 there was a major earthquake that destroyed many homes in Tenochtitlán. Using as a pretext the insulting behavior of a few Tlatelolcan citizens, Axayacatl invaded his neighbor, killed its ruler, Moquihuix, and replaced him with a military governor. The Tlatelolcans lost any voice they had in forming Aztec policy. Axayacatl largely dedicated his twelve-year reign to consolidating his militaristic repute: he led successful campaigns against the neighboring altepetl of Tlatelolco in 1473 (see Battle of Tlatelolco) and the Matlatzinca of the Toluca Valley in 1474, but was finally defeated by the Tarascans of Michoacán in 1476.

The Battle of Tlatelolco was fought between the two pre-Hispanic altepetls (or city-states) Tenochtitlan and Tlatelolco, two independent polities which inhabited the island of Lake Texcoco in the Basin of Mexico. The war was fought between Moquihuix (or Moquihuixtli), the tlatoani (ruler) of Tlatelolco, and Axayacatl, the tlatoani of Tenochtitlan. It was a last-ditch attempt by Moquihuix and his allies to challenge the might of the Tenochca, who had recently cemented their political dominance within the empire. Ultimately the rebellion failed, resulting in the death of Moquihuix who is pictured in the Codex Mendoza tumbling down the Great Temple of Tlatelolca. As a result of the battle, Tlatelolco was subsumed by Tenochtitlan, removed of its privilege and required to pay tribute to Tenochtitlan every eighty days.

Most sources agree that Tizoc took power in 1481 (the Aztec Year "2 House"), succeeding his older brother. Although Tizoc's reign was relatively short, he began the rebuilding of the Great Pyramid of Tenochtitlan (a task completed by his younger brother in 1487), and also put down a rebellion of the Matlatzincan peoples of the Toluca Valley. According to the Codex Mendoza, during Tizoc's reign the āltepēmeh of Tonalimoquetzayan, Toxico, Ecatepec, Cillán, Tecaxic, Tolocan, Yancuitlan, Tlappan, Atezcahuacan, Mazatlán, Xochiyetla, Tamapachco, Ecatliquapechco and Miquetlan were conquered. His rule was marred by the humiliation he received in his coronation war: fighting the Otomies at Metztitlan he brought home only 40 prisoners for sacrifice at his coronation ceremony. After this defeat Tizoc had to fight principally to maintain control of the already conquered territories, and failing to subdue new towns he was replaced, possibly poisoned, by his younger brother Ahuitzotl.

Perhaps the greatest known military leader of pre-Columbian Mesoamerica, Ahuizotl began his reign by suppressing a Huastec rebellion, and then swiftly more than doubled the size of lands under Aztec dominance. He conquered the Mixtec, Zapotec, and other peoples from Pacific Coast of Mexico down to the western part of Guatemala. Ahuizotl also supervised a major rebuilding of Tenochtitlan on a grander scale including the expansion of the Great Pyramid or Templo Mayor in the Year 8 Reed

The Tempo Mayor is finished and inaugurated with the sacrifice of 20,000 captives. The temple was called the Huēyi Teōcalli in the Nahuatl language. It was dedicated simultaneously to Huitzilopochtli, god of war, and Tlaloc, god of rain and agriculture, each of which had a shrine at the top of the pyramid with separate staircases. The spire in the center of the adjacent image was devoted to Quetzalcoatl in his form as the wind god, Ehecatl. The Great Temple devoted to Huitzilopochtli and Tlaloc, measuring approximately 100 by 80 m (328 by 262 ft) at its base, dominated the Sacred Precinct. Construction of the first temple began sometime after 1325, and it was rebuilt six times. The temple was destroyed by the Spanish in 1521 to make way for the new cathedral.

Christopher Columbus reached the island of Hispañola on his first voyage, in December 1492. On Columbus' second voyage in 1493, the colony of La Isabela was built on the northeast shore. Isabela nearly failed because of hunger and disease. In 1496 Santo Domingo was built and became the new capital. Here the New World's first cathedral was erected, and for a few decades, Santo Domingo was also the administrative heart of the expanding empire. Before they embarked on their prosperous endeavors, men like Hernán Cortés and Francisco Pizarro lived and worked in Santo Domingo.

Moctezuma was the ninth Tlatoani of Tenochtitlan and the sixth Huey Tlatoani or Emperor of the Aztec Empire, reigning from 1502 or 1503 to 1520. After his coronation he set up thirty-eight more provincial divisions, largely to centralize the empire. He sent out bureaucrats, accompanied by military garrisons. They made sure tax was being paid, national laws were being upheld, and served as local judges in case of disagreement. In 1517, Moctezuma received the first reports of Europeans landing on the east coast of his empire; this was the expedition of Juan de Grijalva who had landed on San Juan de Ulúa, which although within Totonac territory was under the auspices of the Aztec Empire.

Accompanied by about 11 ships, 500 men, 13 horses, and a small number of cannons, Cortés landed on the Yucatán Peninsula in Mayan territory.

Conquistador Hernan Cortes and his Spanish troops did not conquer the Aztec Empire on their own. They had allies, with the Tlaxcalans being among the most important. As conquistador Hernan Cortes was making his way inland from the coast on his audacious conquest of the Mexica (Aztec) Empire, he had to pass through the lands of the fiercely independent Tlaxcalans, who were the mortal enemies of the Mexica. At first, the Tlaxcalans fought the conquistadors viciously, but after repeated defeats, they decided to make peace with the Spanish and ally with them against their traditional enemies. The aid provided by the Tlaxcalans would eventually prove crucial for Cortes in his campaign.

In October 1519, Spanish conquistadors led by Hernan Cortes assembled the nobles of the Aztec city of Cholula in one of the city courtyards, where Cortes accused them of treachery. Moments later, Cortes ordered his men to attack the mostly unarmed crowd. Outside of town, Cortes' Tlaxcalan allies also attacked, as the Cholulans were their traditional enemies. Within hours, thousands of inhabitants of Cholula, including most of the local nobility, were dead in the streets. The Cholula massacre sent a powerful statement to the rest of Mexico, especially the mighty Aztec state and their indecisive leader, Montezuma II.

Cortés' army entered the city on the flower-covered causeway from Iztapalapa, associated with the god Quetzalcoatl. Cortés was amicably received by Moctezuma. The captive woman Malinalli Tenépal, also known as Doña Marina, translated from Nahuatl to Chontal Maya; the Spaniard Gerónimo de Aguilar translated from Chontal Maya to Spanish. Moctezuma gave lavish gifts of gold to the Spaniards which, rather than placating them, excited their ambitions for plunder. In his letters to King Charles, Cortés claimed to have learned at this point that he was considered by the Aztecs to be either an emissary of the feathered serpent god Quetzalcoatl or Quetzalcoatl himself – a belief which has been contested by a few modern historians.

The wealth of Tenochtitlan was astounding, and Cortes and his lieutenants began plotting how to take the city. Most of their plans involved capturing Montezuma and holding him until more reinforcements could arrive to secure the city. On November 14, 1519, they got the excuse they needed. A Spanish garrison left on the coast had been attacked by some representatives of the Mexica and several of them were killed. Cortes arranged a meeting with Montezuma, accused him of planning the attack, and took him into custody. Amazingly, Montezuma agreed, provided he be able to tell the story that he had voluntarily accompanied the Spanish back to the palace where they were lodged.

The Massacre in the Great Temple, also called the Alvarado Massacre, was an event on May 22, 1520, in the Aztec capital Tenochtitlan during the Spanish conquest of Mexico, in which the celebration of the Feast of Toxcatl ended in a massacre of Aztec elites. While Hernán Cortés was in Tenochtitlan, he heard about other Spaniards arriving on the coast and Cortés was forced to leave the city to fight them. During his absence, Moctezuma asked deputy governor Pedro de Alvarado for permission to celebrate Toxcatl (an Aztec festivity in honor of Tezcatlipoca, one of their main gods). But after the festivities had started, Alvarado interrupted the celebration, killing all the warriors and noblemen who were celebrating inside the Great Temple. The few who managed to escape the massacre by climbing over the walls informed the community of the Spaniards' atrocity.

Cortes returned to a palace under siege. Cortes could not restore order, and the Spanish were starving, as the market had closed. Cortes had a reluctant Montezuma hauled to the roof of the palace, where he pleaded with his people to stop attacking the Spanish. Enraged, the people of Tenochtitlan threw stones and spears at Montezuma, who was badly wounded before the Spanish were able to bring him back inside the palace. According to Spanish accounts, two or three days later, on June 29, Montezuma died of his wounds.

La Noche Triste ("The Night of Sorrows", literally "The Sad Night") was an important event during the Spanish conquest of the Aztec Empire, wherein Hernán Cortés, his army of Spanish conquistadors, and their native allies were driven out of the Aztec capital, Tenochtitlan. Francisco López de Gómara, who was not himself an eyewitness, estimated that 450 Spaniards and 4,000 allies died.

The Spanish invaders who managed to escape from Tenochtitlan were weak, dispirited and wounded. The new Emperor of the Mexica, Cuitláhuac, decided that he had to try and crush them once and for all. He sent a large army of every warrior he could find under the command of the new cihuacoatl (a sort of captain-general), his brother Matlatzincatzin. On or about July 7, 1520, the two armies met in the flatlands of the Valley of Otumba. Spotting the brightly dressed Matlatzincatzin and his generals at the other end of the battlefield, Cortes decided on a risky move. Summoning his best remaining horsemen (Cristobal de Olid, Pablo de Sandoval, Pedro de Alvarado, Alonso de Avila and Juan De Salamanca), Cortes rode at the enemy captains. The sudden, furious assault took Matlatzincatzin and the others by surprise. The Mexica captain lost his footing and Salamanca killed him with his lance, capturing the enemy standard in the process. Demoralized and without the standard (which was used to direct troop movements), the Aztec army scattered. Cortes and the Spanish had pulled out a most unlikely victory.

The introduction of smallpox among the Aztecs has been attributed to an African slave (by the name of Francisco Eguía, according to one account) but this has been disputed. From May to September, smallpox spread slowly to Tepeaca and Tlaxcala, and to Tenochtitlán by the fall of 1520. At this time, Cortes was returning to conquer the city after being thrown out on the Noche Triste. Cortes names only one indigenous leader who died of smallpox, Maxixcatzin. However, Cuitláhuac and other native rulers also died of smallpox. Chimalpahin reports the death of some lords in Chalco from the disease as well. These deaths were part of a widespread epidemic which decimated the common population. Estimates of mortality range from one-quarter to one-half of the population of central Mexico.

The Fall of Tenochtitlan, the capital of the Aztec Empire, was a decisive event in the Spanish conquest of the Aztec Empire. It occurred in 1521 following extensive manipulation of local factions and exploitation of pre-existing divisions by Spanish conquistador Hernán Cortés, who was aided by the support of his indigenous allies and his interpreter and companion La Malinche. Although numerous battles were fought between the Aztec Empire under Cuauhtémoc and the Spanish-led coalition, which was itself composed primarily of indigenous (mostly Tlaxcaltec) personnel, it was the siege of Tenochtitlan—its outcome probably largely determined by the effects of a smallpox epidemic (which devastated the Aztec population and dealt a severe blow to the Aztec leadership while leaving an immune Spanish leadership intact)—that directly led to the downfall of the Aztec civilization and marked the end of the first phase of the Spanish conquest of the Aztec Empire.

Today the legacy of the Aztecs lives on in Mexico in many forms. Archeological sites are excavated and opened to the public and their artifacts are prominently displayed in museums. Place names and loanwords from the Aztec language Nahuatl permeate the Mexican landscape and vocabulary, and Aztec symbols and mythology have been promoted by the Mexican government and integrated into contemporary Mexican nationalism as emblems of the country.

Aztec culture and history has been central to the formation of a Mexican national identity after Mexican independence in 1821. In 17th and 18th century Europe, the Aztecs were generally described as barbaric, gruesome and culturally inferior. Even before Mexico achieved its independence, American-born Spaniards (criollos) drew on Aztec history to ground their own search for symbols of local pride, separate from that of Spain.