I’m working on a lecture that will explain how Islam reached Spain, though I can give you a brief version right now.

Basically, during the Umayyad Caliphate the Muslim Empire continued to expand until it reached the tip of North Africa, modern day Morocco. The Muslim armies then crossed the Strait of Gibraltar. In fact, the word “Gibraltar” comes from the Arabic phrase “Jabal Tariq” or “The Mountain of Tariq” as the Muslim general of this army was named Tariq.

The Muslims then proceeded to conquer most of the Iberian Peninsula (modern day Portugal and Spain) and were only stopped from conquering France by Charlemagne. By this time however, the Muslims were not really interested in conquering France as they were more occupied with the sunny and fertile lands of Spain. They saw France as being too cold and barren to put much effort into.

Also, the Muslim Caliphate was falling apart. The Umayyads were overthrown by the Abbassids and much of the Muslim empire fell apart.

I’ll have to look a little further into the Muslim conquest of India, Inshallah but I’ll try to get back to you. For a good book to read look at the options I’ve listed in the article above.