5,000 years of religious encroachment in 90 seconds

There's an excellent map on Maps of War that shows the spread of the major religions over the past 5,000 years. This map makes me wonder,

in which ways are these religious conquests the result of viral memes and in which ways the organic consequence of imperialist expansion?

in which way is this map misleading by showing geographical spread rather than population spread? What other format could more accurately convey this?

in the case of memetic spread, what makes one religion more successful than others?

given that we are now in the age of memetic globalization, how is religion spreading today?

how could this map be adjusted to show the internal and minority religious influences, including atheism?

[found on Arbitrary Remarks]