Historical Causes of Diffusion
Before the internet or air travel, ideas could only move as fast as people, goods, and messages could physically travel — which shaped how, and how slowly, culture spread for most of human history.
Trade networks were among history’s most powerful diffusion channels. The Silk Road, connecting East Asia to Europe for centuries, carried far more than goods — religions, technologies, and ideas moved along it too, diffusing between cultures that might otherwise never have made contact.
Colonization and military conquest spread culture in both directions at once: colonizers and conquerors relocated to new territories and imposed their own language, religion, and customs (a large-scale case of relocation diffusion), while simultaneously being exposed to the customs of the people they conquered. Religious missionary activity worked alongside trade and conquest to spread universalizing religions like Buddhism, Christianity, and Islam across huge distances over many centuries.
The common thread across all of these mechanisms is speed — or the lack of it. An idea couldn’t travel faster than the caravan, ship, or army carrying it, which is why historical diffusion typically took generations to cross a continent. That hard limit is exactly what modern technology has since removed, which is the focus of the next topic.