Why did Pizarro and his force attack the Luca and capture their emperor, atahualpa

Atahualpa, also Atahuallpa, Atabalipa (in Hispanicized spellings) or Atawallpa (Aymara and Quechua) [2][3] (c. 1500-26 July 1533) was the last Sapa Inca (sovereign emperor) of the Inca Empire (Tawantinsuyu) before the Spanish conquest. Atahualpa became emperor when he defeated and executed his older half-brother Huáscar in a civil war sparked by the death of their father, Inca Huayna Capac, from an infectious disease (possibly smallpox).[4]

During the Spanish conquest, the Spaniard Francisco Pizarro captured Atahualpa and used him to control the Inca Empire. Eventually, the Spanish executed Atahualpa, effectively ending the empire. Although a succession of several emperors who led the Inca resistance against the invading Spaniards claimed the title of Sapa Inca as rulers of the Neo-Inca State, the empire began to disintegrate after Atahualpa's death.