>>17935416
The roots of their rise to power was the abandonment of the previous biggest city in Central Mexico due to a volcanic eruption, which allowed them to absorb its fleeing population, afterwards i think it was just a matter of growing more food to have more people so that they could send them on military and diplomatic expeditions to control trade routes and even invite in foreigners from places like Oaxaca and the Maya area to live with them

The burning was presumably due to either internal rebellion or foreign attack. We'll probably never know since the Teotihuacanos actively preferred pictographic glyphs over fully developed writing and their massive cultural legacy made every other subsequent Mesoamerican civilization outside the Maya area feel the same way