Barriers can have different purposes though. e.g. One wall might be built because the people on one side want nothing to do with the other. Another might be b

Barriers can have different purposes though. e.g. One wall might be built because the people on one side want nothing to do with the other. Another might be built because the people on both sides are in a close economic relationship, but somebody else entirely wants to funnel that through choke points where intercourse can be taxed, monitored for information, etc..