
Really? You are taught this? I'm sure some of it is correct, in areas where religion has not been definied or was in the form of paganism or polytheism, but let's tell both sides of the story.
Islam spread with the expansion of the Arab Empire (an undeniable fact), which was a military expansion. So it was a case of we will sack your towns, take your land and possessions, and if you don't mind converting to Islam that would be awfully kind of you. What a touching story! Suggesting that the Arab states were quite happy to stay where they were, not expand and only reacted to provocation is absolute nonsense. There are numerous accounts of Arab caliphates attacking Christian and indigenous held areas of Africa and southern Europe with the desire for land and treasure. This is what happens with any empire, because it is Islamic it is no different. They are not angels when it comes to direct conflicts in the middle east, eastern Europe, Africa and southern Europe. When the original Arab Caliphate formed after the death of the prophet Muhammed they turned their attentions straight to the richest and most strategic region states; Iraq and Syria and expanded from there, aided by the crumbling Byzantine Empire and it's Persian foes.
It's like other kinds of complete rule, like what happened in Roman Britain and other areas, the invaders get their foot in the door and take a 'softly, softly' approach to dealing with the locals, integrate into their society and then over a couple of centuries turn it completely into their society. It's origin is war and bloodshed.