Put yourself in his shoes. Where are his
recruits coming from? Here are figures for the nearby countries expresses as recruits per million
Muslims:
Jordan 318, Saudi Arabia 110, Palestine 28, Turkey 13, and Eqypt 4.
Here are yields from major Western countries: UK 260, France 200, US 115, Spain 100, Germany 60, Italy 30
Now where would you focus your recruitment efforts? The nearby countries are all Muslim majority countries and, except for Turkey, Arabic. ISIS is probably already reaching most of those who will resonate with his message in these countries. Apparently his message simply does not resonate with young disaffected Turks or Egyptians. But look at the yields from Western countries. Two of them exceed that from Saudi Arabia and the yield from the US is about the same.
So al Baghdadi talks about how Europe is a key part of his plans, invoking Rome (the capitol of Western Christendom; the Eastern capitol having already been conquered in 1453) and Spain, the location of the only Arab-Islamic intrusion into Europe; halted by Charles Martel in 732. Remember this guy is a Ph. D. With this and the new US war, maybe he thinks he can bump up Western recruitment considerably. It won't yield too many bodies: Muslim population in the West is only two-thirds that of Saudi Arabia. So far, total recruits from the West have been about the same as those from Saudi Arabia. I don't think he has a problem getting Syrian or Iraqi recruits. I think he wants Westerners for propaganda purposes (note that the head chopper is a Brit) and maybe some for media skills.