Different topic here, so I decided to continue in a new thread:

Quote Originally Posted by kgauck View Post
There is a period in late antiquity, lets say after Alexander, when religion seemed to become syncretic, and the Greeks tried to identify which Egyptian (or wherever) god was the Nile version of which Olympian.
Interesting take here, Kenneth.
I wouldn't exactly term Alexander as 'late antiquity', but that's a different debate.
However, religious syncretism arose after cultural contact, often after large-scale conquests, the pantheons in question were unique at least to begin with. In the Roman Empire, a number of cults became popular and spread throughout the empire by appealing to a particular clientèle. For instance, the worship of Mithras appealed to soldiers and spread throughout the legions, while the cult of Isis, the Egyptian love goddess, became popular with the 'decadent' upper class.
In BR, Cuiraécen might become popular with Rjurik warriors after the Anuirean conquests, while Haelyn might appeal to Rjurik rulers intent on increasing and cementing their power base. This means I see syncretism as certainly possible due to one church/religion spreading its influence, but still dislike it as existing from the beginning.

As a side note, it seems to me that the Romans had a concept of gods having a regional influence, i.e. they acknowledged that a particular god, a Celtic tribal god for example, held influence in the region where he was worshipped, and therefore deemed it wise to venerate or placate this god, when they were in that region.

Quote Originally Posted by kgauck View Post
Many of the other cultures they encountered were other Indo-European cultures, with many of the same myths and gods, just with different names and some different cultural elements.

In Birthright, like the indo-Europeans, you have a group of related cultural groups, who may have one common origin, and a shared religion.
Hmm, while there may be similarities and common origins, when Roman or Greek writers described other cultures, they usually depicted them as so alien, that I don't think a contemporary observer would make the connection that these cultures shared a common heritage. Some descriptions might also be influenced by trying to explain an unknown phenomenon in the context of the writer's own knowledge and beliefs or by what the writer expects to find.
For example when Vasco da Gama arrived in India, he expected to find Christians, in accordance with medieval legends. His board book describes a visit to a Hindu temple as visiting a Catholic church, if a strange one.

With regard to BR, we are not given very much information on the early history of the human tribes before the flight, so the relations between them are essentially what you want them to be. A loose connection or common heritage is certainly a solution.