Who led the Inca to the decline of the Inca?

The Spaniards led to the decline of the Inca civilization. The Spaniards took Atahualpa (ruler at the time,) hostage and killed his brother Huascar. Then they installed a new leader Atahualpa's brother, Manco Inca. He eventually passed on the throne to his son Tupac Amaru. When the Spaniards captured and executed him, the Inca's resistance to the Spaniards ended.