Answer:
GEOGRAPHY
Step-by-step explanation:
This is from the book titled: "Guns, gems and steel: The Fates of Human Societies"
The one factor that allowed Europeans develop a system to conquer vast portions of the world is "GEOGRAPHY".
This is because it helped them in farming by possessing the most productive crops and animals including allowing the Europeans to develop guns, germs & steel, which ultimately helped to conquer the world.