Things are always moving, even when they seem to stand still. History unfolds, ideas grow, technology develops, culture shifts. When different things are thrown into the mix, things tend to change even quicker. The most burgeoning ages are also the ones where contact among different people was high.
Heterogeneity leads to cultural change.
The Hellenistic period was an age of great intellectual vigour and cultural change. It was also an age of networking, with the various cultures of the Mediterranean coming into contact more than ever before. The Roman Empire developed the existing exchange networks, making it possible for even more people of different cultures to find themselves together in the same room.
The European age of universities, starting in the early 13th century, was disruptive because of the new ideas promoted in the classroom. But the classroom was different. Students came from around the continent, with Latin and Christianity as the only shared cultural capital. Ideas were burgeoning in intellectual centres which brought people of different cultures together, like Toledo, Palermo, Acre.
The Crusades may have been Europe’s biggest ‘diversity and exclusion’ experiment. For all the killing which they involved, the Crusades were also an opportunity for contact, sharing and exchange. The European cultures came out of it transformed. Once planted, ideas can’t be unplanted. They grow to be healthy trees or poisonous ivy, but grow they do.