Fall of the samurai - why do factions change allegiance?

[Dday23456]

When I play the Shogun side, my allies often change allegiance to Imperial. Why is that? It really annoys me. For example the northernmost faction, they keep switching sides and causing me to get attacked from both north and south, which is seriously frustrating.

[Dday23456]

Is it possible to prevent them from switching sides and if so how?

[Sporeduck]

It really isn't - maybe aside from forcing their provinces to your allegiance using the top tier police stations.

It is natural for them to change allegience - the timeframe was really chaotic in that regard. The "join the winning side" train of thought seems to rule here - vassals don't always accept your allegiance either, so you're forced to re-attack them.

[reverie7]

In my Satsuma game, Tosa joined the Shogunate and attacked me. Ten turns later I landed an invasion on his island and conquered it within a year. Think of it as a free casus belli(reason for war) for you to take their lands.

[the04dude]

I've often seen factions switch allegiance as a punishment for not joining their alliance earlier in the game...