Erm...that might be wee a bit 'christo-entric' friend. There was a number of phophets (including Jesus) that influenced Islam. Maybe more so. In Koranic references to Jesus, it warns that his divinity is false by saying,
"People of the book, do not trangrees the bounds of your religion. Speak nothing but the truth of God. The messiah, Jesus the son of Mary, was no more than God's apostle..."
I think they would have got along just fine without him. Sorry.
Johanus.
Mecca, up until the early 600's, was a city of the Quraysh tribal alliance, as well as an ancient holy site for other Arabic tribes, and the main overland commercial hub in all Arabia. It was also home to respectable numbers of Christian and Jewish converts in the area. Khadijah, Mohammed's first wife, may have been a Christian herself. And some Arabs that followed neither religion, called Hanifs, were monotheistic. But Christianity and Judaism both have scripture and doctrine, so its not disputible where the founder of Islam got most of his material from.
And for those of you whom think that the armies of Islam would just bulldoze their way through Europe if it weren't for Christianity; thats a load of crap. Islam's rapid military expansion was due in large part to the fact that both the Byzantine and Sassanids in the west and east were in economic meltdown, due to the wars in previous decades. Egypt, Palestine and Syria was a hotbed of different Christian heresies, which were difficult for the Orthodox Nicene Church to contain. And just as was the case in the Sassanid Empire, central authority was weakening, and the population was made impoverished by over-taxation.
It seems also that some of the natives of Syria, Palestine, and Egypt, had initially thought of Islam as another kind of Christianity. In any case, the Arabs were tolerant of their faiths by necessity. Plus, the Caliphs needed the local upper-classes to recruit as bureaucrats and secretaries.
After that, the conquest of much of North Africa was helped by the logistics of ships from Syria and Egypt and the durable Arabic Dromedaries that supplied the Arabic forces fighting the Byzantine Exarchate of Carthage, and the disparate Berber tribes.
And the Visigothic Kingdom in Spain was unstable, due to being ruled by a small minority of Germanic-descendent nobility, the fact that they largely practiced different kinds of Christianity for so long, and because the wars of reconquest instigated by the Eastern Emperor Justinian was damaging to them as well.
In many ways, the fratricidal relations between different Christian ideologies was one recipe for internal division.