Asklemmy

Well the most common and effective way of destroying local cultures, is to force the people to speak the common language.

For example in France, the UK, and many other places, there used to be many local regions, with their own languages and strong local cultures and loyalties. The rulers wanted to kill the local cultures, so that the people would have no local identity. This stops disloyalty or independent thinking or independence movements.

They did this by forcing their subjects to speak a common language.

This policy was perfectly effective.

A province speaking its own language can easily maintain its own identity and push for independence. Without its own language this is more difficult, even if it keeps its own customs.

I think I've been too vague. So I can elaborate about these policies in the UK or France, if you like. For other territories (Spain, Italy, etc) I believe the same thing happened but I'm not the expert.

How would you define "culture"?

What is "a culture"?

Maybe not a single common language, but there needs to be a limited set at least. People have to be able to have person-to-person conversations. Maybe that takes the form of a few languages where people are fluent in enough languages that they can speak at least one of the same languages as another person they meet. Or a perhaps there are local languages, with a single lingua franca. Then there's the easiest, where there is one dominant language that is spoken by nearly everyone, at least to some extent. Personally I kind of prefer the lingua franca approach, but I wish a constructed language would finally gain wider popularity. Could be Esperanto, could be something that took some lessons from the imperfections in Esperanto.

Yes, so we can talk to each other.

It has a strong effect on it. A lack of a common language makes it more likely for a culture to fragment, and a widespread common language causes it to grow closer together. I wouldn't say it's essential though.

Kies kulturo?