Why were Muslim forces able to take control of India?

Answer:

When Muslims are true to their faith, they can conquer anyone. God says, in the Qur'an, that anyone who worships other than the One God is weak. They do not have the help of God and, so, will be conquered easily. The reason Muslims are themselves conquered today is simply because they are not true Muslims. They are weak and hyppocritical - or they are extremists who kill innocent people. So they do not have the help of God.

www.freequran.org