The most important religious site in the world and for non-muslims visits are highly restricted but still possible on the grounds.
That in part was what all of the crusades were about. At one time the muslims military was quite powerful. In southwestern europe they were stopped by charles martel in France and they ruled Iberia for centuries. The Christian forces just did not have the power. IIRC in the 17 century the turks were stopped at the gates of Vienna (Siege of Vienna, (July 17–Sept. 12, 1683) .That would be one big cat kabob if I'd been there to see that thing tearing up a 2000 year old wall