The Huns, and the Mongols later on, placed little importance on religion. Both of these groups had advanced military techniques, and were able to conquer other civilizations. But they were also both absorbed by those very civilizations that they conquered. The argument can be made that strength of religion was a major reason that these civilizations, such as China and India, were able to hold out against an invading culture.
Basically, can anything win out against religious fervor?