Question: What people group established an empire in the valley of mexico?

Disambiguated questions and answers:
context: The valley has been inhabited for at least 12,000 years, attracting humans with its mild climate (average temperatures between 12 and 15 °C, or 54 and 59 °F), abundant game and ability to support large-scale agriculture. Civilizations that have arisen in this area include the Teotihuacan (800 BC to 800 AD) the Toltec Empire (10th to 13th century) and the Aztec Empire (1325 to 1521). When the Spaniards arrived in the Valley of Mexico, it had one of the highest population concentrations in the world with about one million people. After the Conquest, the Spaniards rebuilt the largest and most dominant city here, Tenochtitlan, renaming it Mexico City. The valley used to contain five lakes called Lake Zumpango, Lake Xaltocan, Lake Xochimilco, Lake Chalco, and the largest, Texcoco covering about of the valley floor, but as the Spaniards expanded Mexico City, they began to drain the lakes' waters to control flooding. Although violence and disease significantly lowered the population of the valley after the Conquest, by 1900 it was again over one million people. The 20th and 21st centuries have seen an explosion of population in the valley along with the growth of industry. Since 1900, the population has doubled every fifteen years. Today, around 21 million people live in the Mexico City Metropolitan Area which extends throughout almost all of the valley into the states of Mexico and Hidalgo.
question: What people group established an empire in the valley of mexico in the 10th century?
short_answers: the Toltec

Toltec
wikipage: Valley of Mexico

context: The valley has been inhabited for at least 12,000 years, attracting humans with its mild climate (average temperatures between 12 and 15 °C, or 54 and 59 °F), abundant game and ability to support large-scale agriculture. Civilizations that have arisen in this area include the Teotihuacan (800 BC to 800 AD) the Toltec Empire (10th to 13th century) and the Aztec Empire (1325 to 1521). When the Spaniards arrived in the Valley of Mexico, it had one of the highest population concentrations in the world with about one million people. After the Conquest, the Spaniards rebuilt the largest and most dominant city here, Tenochtitlan, renaming it Mexico City. The valley used to contain five lakes called Lake Zumpango, Lake Xaltocan, Lake Xochimilco, Lake Chalco, and the largest, Texcoco covering about of the valley floor, but as the Spaniards expanded Mexico City, they began to drain the lakes' waters to control flooding. Although violence and disease significantly lowered the population of the valley after the Conquest, by 1900 it was again over one million people. The 20th and 21st centuries have seen an explosion of population in the valley along with the growth of industry. Since 1900, the population has doubled every fifteen years. Today, around 21 million people live in the Mexico City Metropolitan Area which extends throughout almost all of the valley into the states of Mexico and Hidalgo.
question: What people group established an empire in the valley of mexico in 1325?
short_answers: the Aztec

Aztec
wikipage: Valley of Mexico

Long answers:
knowledge: content: The Valley of Mexico (Spanish: Valle de México) is a highlands plateau in central Mexico roughly coterminous with present-day Mexico City and the eastern half of the State of Mexico.
wikipage: Valley of Mexico
long_answer: Several people groups established an empire in the Valley of Mexico in central Mexico, including the Toltec people, who did in the 10th century, and the Aztec people, who did in 1325.