[Cronos]

The vast majority of Jews and Arabs never converted to Christianity

Not really true -- Egypt was mostly Christian by the 6th century -- as was Syria, Western Mesopotamia, Turkey etc. In the Arabian peninsula you had Arians and Nestorians Christians preaching, while in India you had St. Thomas' Christians right from the 1st century.

In fact Christians were in the majority in Islamic lands well into the Crusades but were slowly ground down by jaziya, persecution etc.

[stripes1776]

Not really true -- Egypt was mostly Christian by the 6th century -- as was Syria, Western Mesopotamia, Turkey etc.

Egypt was part of the Roman Empire which was Christian. Asia Minor (Turkey) was part of the Roman Empire too and therefore Christian. We have already covered that, didn't we?

In the Arabian peninsula you had Arians and Nestorians Christians preaching,

Yes, we have already established that Christians were present in the Arabian peninsula. My point is this: Christianity did not strike deep roots in Arabia and those roots were easily pulled up by Muhammad and his followers. And you disagree with that statement.

while in India you had St. Thomas' Christians right from the 1st century.

Thomas made few converts. Not only were the roots shallow in India, but they were sparse as well. We know that some churches were established even further east in China, but there were few converts. Christianity withered away in China.