It was actually the fact that the people with boats also lived in an area where carbon-rich iron was in the ground all over the place. While other civilizations first needed to discover and perfect metallurgy, Europeans only needed to mine it and work it into shape to have superior weapons and armor than the rest of the world.

Basically, Europe got the best spawn location, used that to gather momentum in the early game, and has been able to preserve that momentum through military dominance throughout the midgame.