- a vast empire that flourished on the western coast of South America from the early 15th century A.D. up until its conquest by the Spanish.

The vast empire you are referring to is the Inca Empire. It flourished in the Andean region of South America, particularly along the western coast, from the early 15th century until its conquest by Spanish conquistadors led by Francisco Pizarro in the 1530s. The Inca Empire was known for its advanced agricultural techniques, extensive road systems, impressive stone architecture such as Machu Picchu, and a complex societal structure that included a centralized government and an efficient economy. At its height, the empire stretched from modern-day southern Colombia to central Chile, encompassing a diverse range of cultures and environments.