Final answer:
Pachacuti's immediate successors were Tupac Inca Yupanqui and Wayna Qhapaq. They expanded the Inca Empire into Ecuador, central Chile, and the edge of the Amazon basin. Their efforts greatly enlarged the empire's territory but also set the stage for its eventual collapse under Spanish conquest.
Step-by-step explanation:
The Inca Empire underwent significant expansion during and after the reign of the first Sapa Inca, Pachacuti. His immediate successors, Tupac Inca Yupanqui and Wayna Qhapaq, played pivotal roles in extending the boundaries of the empire. Tupac Inca Yupanqui, ruling from 1471-1493 after Pachacuti, aggressively continued conquests to the north, securing territories such as the Kingdom of Quito. He also faced staunch resistance in the south, which marked the southern limits of Inca expansion at that time.
Following Tupac Inca Yupanqui, Wayna Qhapaq further expanded the empire eastward into the Amazon basin and further north into Ecuador. During his reign, the Inca Empire experienced significant growth, but it also faced the challenges of costly wars and the sharpening of military skills. Unfortunately, his reign and the might of the Inca Empire met their demise with the arrival of the Spanish conquistadors, resulting in the rapid decline and fall of the widespread state that once dominated from Ecuador to northern Chile.