Conversation so far:
who was the Inca ruler who greatly expanded the inca empire under his rule
with the arrival of the first great Inca leader Pachacuti Inca Yupanqui and the defeat of the Chanca in 1438 CE, the Incas began expanding south and in all directions.
who was the successor to Pachacuti Inca Yupanqui.
Thupa Inca Yupanqui, Pachacuti's successor from 1471 CE, is credited with having expanded the empire by a massive 4,000 km.

Question: when was the fall of the civilization
Self-contained rewrite: when was the fall of the Inca ivilzation