Didn't say that the so-called Dark Ages were caused by a single factor, but there was a primary factor and that was the jihadist invasions known as the Islamic conquests. I suggest you look over these works since they go into more detail:
As for the treatment of minorities, are you familiar with treatment of dhimmis under Islam? You can examine these texts for more: http://www.amazon.com/Islam-Dhimmitude-Where-Civilizations-Collide/dp/1611472369. The treatment of minorities under Islam was always in flux depending on the location and who was in charge. Jews may have been treated better than the Christian and pagan populations of Europe, but there were intermittent persecutions against them too, just as there were persecutions against Christians.
As for trade, read what happened to the papyrus supply being cut down and how it affected literacy in Europe. This was noted by historian Henri Pirenne in the 1930s.
As for 1453 and later, that is hundreds of years after the events I'm discussing, so it's not relevant here.
