In short answer, why is the West the "dominant" force in the World. (depends how you define dominant).

1) Read a book called "Guns Germs and Steel" - to my mind basically explains it. btw Religion has NOTHING to do with it.
2) Islam starts in what 620 - 630 AD, Christianity had a bit of a head start.
The current Islamic year is 1428, (this reckoning starts in 662AD I believe).
I am sure in 1428 Western Europe had some issues with Christian zealots - Ever heard of the Inquistion ? Makes Al-Qiaida look like kindergarten novices.