What "large enough army" did you have in mind to convert the ME to Christianity and what would you have them do? What size of an army and methods were needed in bringing down communism in the Soviet Union? Or would be needed to achieve the same in China over, say, the next 50 years? The point is, you don't need these "large armies" to convert communists. The peoples of these countries are not communists by choice.
So. You can have a non-communist China in short order, and without an army and a brigade high-priests of any kind - simply give them the choice!