On a similar line:
http://www.danielpipes.org/article/4227
I'd add to the list above the decadence of Christianity. When everybody believes to be living in a post-Christian world where religion is a thing of the past, Islam is absorbed by osmoses and sucked in by vacuum as a return to the old principles. Plus, as a Muslim you are useful to the ruling and power-hungry classes, tolerated by the population zombified by PC which combined grants you a bunch of priviledges.
The gravest mistake of the projections of a possible Muslim majority in Europe, like that of SUBMAN for example, is to consider that Islam only expands by breeding. This is a most elementary error. If that was the case Islam would've never surpassed Judaism and it would've never left the Middle East. That's not the case and the amount of Muslims that exist today was achieved by conversion. Islam would grow in Europe not only out of demographic expansion but out of the conversion of the Europeans who sought the fundaments that were abandoned by the Christian Churches. Ask Konovalov.