wait.... WHAT.
I thought AI was hardcoded not to be able to break alliance during a war. Heck, they don't during a bankruptcy.
WTF.
Anyhow, did ottomans get new ruler that is militarist, and previous one was administrator? Did opinion with ottomans fall below 100 after new king took throne? if that is case, they CAN go hostile and break alliance over wanting your neighbouring land.
but during a war? never seen that.
anyhow, if you ally militaristic nations like burgundy or ottomans, ALWAYS try to keep relations above 100. they can't go hostile then.
Want your provinces modifier scales if their miitary rating is lot better then yours, but I think you did not increase relations enough? Surely wants your provinces wasn't more then -100 right?
either that, or they broke alliance over sharing vital interest. militarists go bonkers on alliances if you got shared vital interest.
who else is rival of ottomans? can you ally russia or france or GBcause of being rival to otto?
They had a diplomatic ruler, but he died a good 10 or so years before this incident. He was replaced by a militarist, who had become increasingly interested in my lands (seriously, he went from wanting only the odd province, to wanting most of Arabia, Persia, and the Horn). As I usually do with fickle alliances, I had a diplomat permanently on the Ottomans, so that we'd never dip below 100 from improved relations, but near the end, we were maxing out at 50-60 relations at peace, thanks to insane maluses for "wanting your provinces". And during the war, that was only bumped up to 80, thanks to the modifier "in war together".
And, having dealt with these kinds of alliances on numerous occasions, I had made sure to keep lands they wanted (and weren't already mine) not marked as my vital interest.
I wish I'd have checked if it cost them a point of stability, since they broke the alliance during a war.
And none of the other great powers in Europe will ally me. Russia is pretty weak iirc, France is rivaled to me, GB hates my guts, and Austria is cleft in twain, and relatively weak. Sweden's not doing so hot, Brandenburg MIGHT make for a good ally, but I don't know. And I'm rivaled to Ming, and Hindustan doesn't like me, either. I'll check on Milan.
Oh, and Morocco is most likely going to break our alliance, since they're allied to the Ottomans. Even though we have 100 trust. When it rains, it pours, I guess. Might end up building a super army and just try and wear them down, if it comes down to it. We're so close to restoring the flames, too.