Spanish conquistadors led by Francisco Pizarro and his brothers explored south from Panama, reaching Inca territory by 1526. It was clear that they had reached a wealthy land with prospects of great treasure, and after one more expedition in 1529, Pizarro traveled to Spain and received royal approval to conquer the region and be its viceroy. This approval was received as detailed in the following quote: "In July 1529 the queen of Spain signed a charter allowing Pizarro to conquer the Incas. Pizarro was named governor and captain of all conquests in Peru, or New Castile, as the Spanish now called the land."

When they returned to Peru in 1532, a war of the two brothers between Huayna Capac's sons Huascar and Atahualpa and unrest among newly conquered territories-and perhaps more importantly, smallpox, which had spread from Central America-had considerably weakened the empire. Pizarro did not have a formidable force; with just 168 men, 1 cannon and 27 horses, he often needed to talk his way out of potential confrontations that could have easily wiped out his party. The Spanish horsemen, fully armored, had great technological superiority over the Inca forces. The traditional mode of battle in the Andes was a kind of siege warfare where large numbers of usually reluctant draftees were sent to overwhelm opponents. The Spaniards had developed one of the finest military machines in the premodern world, tactics learned in their centuries' long fight against Moorish kingdoms in Iberia. Along with this tactical and material superiority, the Spaniards also had acquired tens of thousands of native allies who sought to end the Inca control of their territories.

Inca expansion (1438-1527)Their first engagement was the Battle of Puná, near present-day Guayaquil, Ecuador, on the Pacific Coast; Pizarro then founded the city of Piura in July 1532. Hernando de Soto was sent inland to explore the interior and returned with an invitation to meet the Inca, Atahualpa, who had defeated his brother in the civil war and was resting at Cajamarca with his army of 80,000 troops.

Pizarro and some of his men, most notably a friar named Vincente de Valverde, met with the Inca, who had brought only a small retinue. Through an interpreter Friar Vincente read the "Requerimiento" that demanded that he and his empire accept the yoke of King Charles I of Spain and convert to Christianity. Because of the language barrier and perhaps poor interpretation, Atahualpa became somewhat puzzled by the friar's description of Christian faith and was said to have not fully understood the envoy's intentions. After Atahualpa attempted further enquiry into the doctrines of the Christian faith under which Pizarro's envoy served, the Spanish became frustrated and impatient, attacking the Inca's retinue and capturing Atahualpa as hostage.

Atahualpa offered the Spaniards enough gold to fill the room he was imprisoned in, and twice that amount of silver. The Inca fulfilled this ransom, but Pizarro deceived them, refusing to release the Inca afterwards. During Atahualpa's imprisonment Huascar was assassinated elsewhere. The Spaniards maintained that this was at Atahualpa's orders; this was used as one of the charges against Atahualpa when the Spaniards finally decided to put him to death, in August 1533.