The correct answers to this question are: 1) the Spanish firing guns into the crowd. 2) The use of charging cavalry, followed by foot soldiers.
The Spanish conquest of the Inca was made possible by the Spanish firing guns into the crowd and the use of charging cavalry, followed by foot soldiers.
The Spaniards had more impressive weapons never before known by the Incans or any Mesoamerican and South American Indian tribe. Those weapons were totally new to them. The Spaniards conquerors also had horses, an animal never before seen by the Incas too.
Another important factor that affected not only the Incas but Native American tribes was the spread of diseases brought by the Spaniards such as Malaria, Influenza, chickenpox, Cholera, among many others.