Final answer:
Based on the excerpt, it can be concluded that the Tepanec Empire was falling apart due to internal struggles and was subsequently defeated by the forces of Itzcoatl and his ally Nezahualcoyotl.
Step-by-step explanation:
The Tepanec Empire was experiencing decline and facing internal turmoil, as identified by the key events during the early 1400s. The death of Tezozomoc, the ruler of the Tepanec Empire, led to a succession struggle which weakened the state, creating an opportunity for Itzcoatl, who formed an alliance with the exiled Acolhua leader Nezahualcoyotl. Together, they were able to topple the Tepanec forces. However, the notion that the Tepanec Empire allied itself with the Acolhua or merged with Itzcoatl's forces is incorrect.
With the founding of Tenochtitlán in 1325 by the Mexica, who later became known as the Aztecs, a period of growth and expansion began. Through strategic alliances and military prowess, the Aztecs eventually dominated central Mexico, forming the Triple Alliance with Texcoco and Tlacopan. This alliance laid the groundwork for the eventual creation of the Aztec Empire.