FoTs Allies changing sides?

[Marchalis]

Any way to prevent them from changing sides?

I was just playing Legendary mode for the first time. An ally held 1/4 the map while I held another 1/4, with some other smaller allies we where close to winning.
Then the big ally just a few years from us winning randomly switched sides for no reason... Sniping my victory away because my lands where all split up around the old ally, and there simply, regardless, aren't enough years left to cover that much map. Meanwhile I can't switch sides because "I've gone too far" lol BS my ally was as far as I was >_<

I think I have to start again and just stomp my allies across the map as fast as I can :(

Any advice?

[BastardSword]

Yeah it is pretty BS and seems completely random, and it's a pretty fake way of creating challenge. In my current campaign I'm Choshu, and by the time I was approaching RD the only imperial forces were me and Satsuma, and the rest of Japan was Shogunate. I was too far along to switch to shogunate. Naturally, Satsuma switched to Shogunate just before RD, meaning I have to take over the whole map.

In the past when this keeps happening to all the clans in my faction, I've just switched sides if I still can. If the game wants to artificially mess with me, I'll exploit it back. You kind of want to rush into RD because then clans stop flipping.

Best thing is to have your side all unified and not switching sides. Then they can help you out by spamming navies, which is about all they're good for because they are useless at taking over provinces.

It kinds seems like this happens more to clans that are at the edge of the map than clans that are in the center. If I'm Tsu or Obama it seems like the other clans in my faction tend to not flip, making RD really easy. But if I'm Saga or Sendai, pretty much all the clans in my faction keep flipping, meaning I have to either flip myself or tediously take over the whole map.