Here’s the real reason for the Arab “explosion” out of the peninsula: the tribes along the Levant were nominally Christian - Monophysites: http://en.wikipedia.org/wiki/Monophysitism - the Ghassanids: http://en.wikipedia.org/wiki/Ghassanids guarded the trade routes. Eventually, the Byzantines attacked the leadership as heretical and Islam was welcoming. Once they became oppressed by Byzantium they decided to switch and depredate the trade routes themselves. Hence Islam, the religion of predation, was a perfect match.
You’ll note that once other people’s money runs out Islam slows down quite a bit.
The Byzantines had for a century or two been persecuting Jews and “heretical” Christians all through the Levant, Egypt and North Africa.
For most of these people, the switch from orthodox Christian to Muslim rule really was an (initial) improvement, economically and for religious freedom, etc.
1500 years later it hadn’t really worked out that way.
Spain had also been indulging in religious persecution of minority groups, who reasonably enough felt little loyalty to their persecutors.
It is interesting that Muslim expansion more or less ran into a brick wall and stopped for centuries when it bumped up against united Christian populations in Italy, France, Anatolia, etc.