There is obviously an ethnic/cultural/geographic factor in the concentrations of religions in certain areas. Where a particular religion is tied in with the culture of an area, it is very much more difficult for a separate religion to get much of a foothold. Missionaries have found this in parts of the world where Christianity was not originally part of the culture for instance. Even protestants have had difficulty in getting into those parts of the world where Catholics were the predominant church group and vice versa (though to a lesser extent) So I would say it is more historical than cultural, but now has become very cultural. Bill |