How did geography impact cultural diffusion in world history?

Where you live can have a large effect on who you are in cultural terms. Let's say you live on a peninsula that has little commerce with the outside world, almost exclusively through the people who live on the mainland nearby. The culture of these people cannot help but affect your customs, your interests, and your culture in general.

Like the old saying, "Show me who your friends are and I will show you who you are."