What Is a Proximal Cause for Why a Small Group

What is a proximal cause for why a small group of Spaniards was able to conquer the Incan empire?

A) The Spaniards had better weapons than the Incans.
B) The Spaniards had more domesticated animals than the Incans.
C) The Eurasian continent stretches largely from east to west,whereas the Americas stretch largely from north to south.
D) The Incans had few species of cultivatable plants in contrast to the Spaniards.
E) The Spaniards were physically stronger than the Incans.