In OTL, at some point early in their history, Muslims switched from facing Jerusalem during prayers, to facing Mecca.
What if the early Muslims never made the switch? Or, if one denomination made the switch, and another denomination did not?
The butterflies on Arabia are enormus. It's been a while since I researched this in depth, but when Muhammed fled to Medina he was partially taken in by the local Jewish Community. Proto-Islamic traditions blended with Jewish ones; Muslims prayed facing Jerusalem, they took friday prayers while the Jews prepared for the Sabbath, etc... But after a period of time, this alliance of faith and convenience began to fall apart. It's hard to say who betrayed whom, as most sources from the timeperiod are Early Islamic and obviously somewhat biased. But regardless of who struck first, Muhammed expelled the Jews from Medina, and rewrote some of his earlier instructions which had been inspired by them.
So Muhammed keeping that pillar of faith directed to Jerusalem would have interesting repercussions. Probably, but not necessarily, it would involve him never expelling the Jews from Medina. That means that the Jews and Muslims will probably be on slightly better terms, and Islam would possibly become slightly more tolerant of non-muslims (at least, people of the book). This could potentially cause butterflies throughout the Arabian penninsula. The repercussions of this during the expansion, even assuming that muhammed's unification goes basically as OTL, will be very interesting. For example, there would probably be a movement among the most faithful to take Jerusalem from the unbelievers. On the other hand, we may be dealing with an islam that is more tolerant to ahl al-kitab, which would make a war against them slightly more difficult to sell. But in the short term, one of the most interesting butterflies may be how this changes what hadiths get passed down. The minor to major changes this will reak on Arabia will quite possibly lead to some of ours being lost, and others becoming accepted as the teaching of the prophet.
Well, I'm not terribly sure but I'll try and guess what will happen. Mecca only loses a small amount of importance and Jerusalem becauses a little more important than Mecca. The Hajj to both Jerusalem and Mecca is required. Since the world's most Important Islamic City is now closer to Europe, Eastern Europe ends up more dominated by Islamic Interests. The Crusades (if not erased by Butterflies) become bloodier and more emotional as hatred between Muslims and Christians increase even more than in the OTL. The Muslims still beat the Christians. The only thing we can know about TTL's Modern Day is that Israel doesn't Exist and Jerusalem is still in the Hands of the Muslims.
Also, sorry if my words come out jumbled. I'm kinda new at this.
Don't worry. For a new user, that is a very coherent and well thought out idea. I don't think I was doing that for a while when I first joined up. Welcome to the board.