According to The Biography Channel, Spanish explorer Francisco Pizarro was able to defeat the Inca easily because the Incans were embroiled in their own civil war and suffering from the smallpox epidemic, both of which had dramatically weakened the Incan empire. This made it easy for Pizzaro to take the last Incan Emperor, Atahuallpa, prisoner and execute him, paving the way for complete conquest.
According to the History Channel, Franciso Pizzaro sailed to Peru in 1531 and reached the Incan town of Cajamarca in November of 1532. After Pizarro persuaded Atahuallpa to meet with him, he ambushed the Incan emperor, killing thousands of his men with the superior weapons of the Spanish army. Atahuallpa was taken prisoner, but he offered to fill a large room with gold in exchange for his release. Pizzaro accepted the gold but put Atahuallpa on trial and had him executed in 1533. Pizzaro was then able to move on to the city of Cuzco, where he conquered the city with little resistance from the weakened Incans. He placed a puppet emperor, Manco Capac in charge and went on to found the city of Lima, in 1535. The following year, Manco Capac attempted one last uprising of the Incans against the Spaniards, but he was quickly defeated and the fall of Incan Empire was complete.