okay, I just finished my game with the Arabs in 1320 via UHV. After defending against the first few ghazi attackers in 850-900 it became a more enjoyable game.
Having the first crusade, the Seljuks and Ghazi attackers from Arabia at the same time is....wow. But feasible, sure. Ghazi vs ghazi (barb) had a much higher success rate than the 70-80% the simulator gave, more around 90% I had the impression. they made defending the homeland not only possible but even interesting.
My strategy for UHV3 (35%) was: wait until Byzantium declares war on someone (usually Bulgaria, Venice or Genova) and join them. This gives you open borders. Use 2 cities to spam missionaries for Byzantium and send 2-5 ghazi / mounted archers towards europe.
There I got lucky and conquered the polish capitol (only defended by 2 archers^^) - this city spammed missionaries nonstop until the Norse became muslims and Germany was almost 50/50 muslim/catholic. After the Lituanian start I also made them completely muslim (although they remained without a state religion) and spread it to some more of Kievs cities.
My last attack was Belgrad which I conquered for Venice & Hungary but by then It was already enough.
Which civs you focus on is secondary (although some like the norse who start without a religion are more susceptible), important is the open borders part with Byzantium (they never cancelled it on me between 1100 and 1320).
There might be a way to reach the 35% spread before europe gets populated but since you have to wait until 1290 anyway I figured the 30 more years are not much of a problem and the game is a lot more relaxed that way.
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edit:
could someone please explain me how to play the first dozen turns as the Ottomans? I didn't settle and instead took Constantinople with my mounted units (you do get some free wins here) and sent the unmounted units from the "eastern" stack out to conquer me 1-2 cities towards the sulfur or horses.
But the Byzantine SoD usually not only takes back Edirne but also completely wipes my "western" stack out. I have nothing to counter their Combat2-3 - Knights. And I need horses or sulfur to produce any useful units. But both of them require me to conquer at least 1 more city which in turn means I won't get the resource in less than 5-9 turns (due to rebellion in the conquered city).
I tried leaving Edirne almost undefended so they take it and I could use the bombards...but still my knights only had ~50-60%chance after 4 bombard-attacks. And I have only 4-5 knights while they have 10+ -.-
Shouldn't their units desert or does that only happen to the human player?
also: while maybe not really a bug it seemed weird and unintented: I started at war with Arabia (vasall of France) but could even get open borders with France but had no way to stop the war against the Arabs...