What causes allies to seemingly randomly cancel their alliance with you? It seems impossible to keep an alliance with another GP for longer than a decade as they'll just cancel the alliance, despite having perfect relations. I just had a game where I was allied with France, joined them in their war against Prussia, sacrificed thousands of my pops to protect their lands, spent untold amounts of money during the war, and then France decides to just up and cancel the alliance 3 years later. I used to think that this sort of thing was caused by conflicting interests or something, but I've had it happen to me several times in each of my games, even when my infamy is low and I'm not going up against their sphere interests. Not that allies are of any use beyond keeping possible attackers at bay, as they just mess with wargoals and white peace at the most inopportune times.