Interesting, the nearest comparison I could make is with Algeria - Franks ruling over Muslims.
I'd assume with the Kingdom being prominently Christian that it would convert people over time, but really, it can't exist in a vacuum. If its survival is tied to the Romans, then there will be more Orthodoxy, if it is tied to Crusaders, then Crusader-Settlers might become a long-lasting phenomenon, perhaps moving into Egypt, North Africa and Mesopotamia over generations.
In my opinion, the most likely scenario is that the Patriarch of Jerusalem becomes a useful political tool. Don't like the Pope? Go to Jerusalem. Ostensibly Catholic, but with a bit of give for Crusaders. Good way to get rid of younger sons or bastards. Give them a sword, and send them east.
With the greater part of Crusaders going to settle in Jerusalem, and defend it, those who are on the offensive might have to resort to partnering with local Christians. I.e. Crusaders working with a Coptic revolt, or a Nestorian Uprising. Having a Christian Patchwork in the East, with an Orthodox Roman Empire, Crusader-Coptic Egypt, Crusader-Nestorian Mesopotamia and a Crusader-Catholic Jerusalem would be a mess, but certainly interesting.
IMHO, the Ottomans would tackle Jerusalem en-passant before tackling Byzantium, long, long before besieging Vienna.
Alright interesting, how might this influence things when the Ottomans rise, if indeed they do?
I doubt that we'd see the Ottomans ITTL, I think we'd probably have to work through a "Crusader Coalition" vs the Turks to begin with. The Ottomans were quite late players in the Turk conquests. If the Seljuks lose Mesopotamia (hard, but not impossible), then they are already on the back-foot.
I think its more likely that the Byzantines would be invading parts of Europe, whilst trying to undermine the Crusader-States so they can take over. Heck, I can't see a fully independent Jerusalem lasting much beyond the 1300s anyway without the Romans having their say. The politics around there are going to be centred around being independent vs pro-Pope vs pro-Constantinople. The Papacy might be able to provide migrants, Constantinople is a direct threat and also a direct support, and independence is free of interference, but vulnerable.
Note, this reliance on Constantinople will fade over time, as demographics stabilise, especially if Mesopotamia can retain its independence, so the Romans will want to take over, or provincialise them all soon. Does a Despotate of Jerusalem count? Essentially a vassal state of the Romans with the King/Despot paying tribute to the Emperor? That would probably be the easiest way to ensure the survival, a King of Jerusalem that is subservient to the Emperor, but allowed to retain its Catholicism is basically the best deal on all sides.
Alright very interesting. So if the kingdom achieved that, and somehow survived to the present day, middle eastern politics would be vastly different, as would the world I imagine.
Okay interesting, would the Mamluks/ Ayyubid dynasty be able to hold back against a resurgent sort of Christian ethos then?
The more I think about it through history the more I find it being ASB for the Crusader state to make it to the present-day. Just dont see it surviving all the attacks by Muslims. I sincerely doubt it can survive Mamluks, Seljuks, Mohammad Ali, and Ottomans along with everything else. And no, just surviving longer than OTL doesn't change history enough to make those players, and especially not Napoleon disappear *no, it doesn't change the laws of probability across the universe! Nappy's dad isn't going to twitch wrong!* if it survives and big ASB what if, to Nappy's day he takes it anyways. In the vacuum left behind as he leaves Muslims take back over. History "converges" with OTL. As it normally SHOULD with minor PoDs that don't affect a large area of history.
A crusader state in Jerusalem will not affect that.That's of course assuming things like Nappy even coming to power
The more I think about it through history the more I find it being ASB for the Crusader state to make it to the present-day. Just dont see it surviving all the attacks by Muslims. I sincerely doubt it can survive Mamluks, Seljuks, Mohammad Ali, and Ottomans along with everything else. And no, just surviving longer than OTL doesn't change history enough to make those players, and especially not Napoleon disappear *no, it doesn't change the laws of probability across the universe! Nappy's dad isn't going to twitch wrong!* if it survives and big ASB what if, to Nappy's day he takes it anyways. In the vacuum left behind as he leaves Muslims take back over. History "converges" with OTL. As it normally SHOULD with minor PoDs that don't affect a large area of history.
A crusader state in Jerusalem will not affect that.