Why my ally Edo is so eager to become imperial and attack me?

[Это не шоколад]

Like wtf, Edo is seat of shogun

[Skyler712]

The same way in vanilla shogun 2 you cant have a "trusted" ally. Never. In shogun 2, every ai clan has something like an "expansion preference". If you and your "ally has not any shared interest in one province, it wouldnt betray you... yet. You have to be powerful to convince it its better to them to expand in another direction. i tested it recently by being ally with chosokabe, they got a rebellion, i conquered it (dude, i needed my ♥♥♥♥♥♥♥ stone ok?), and after 5 turns they throw a 60 turn alliance in the sewer.

Now for the FOTS: Similar here. In addition to what i ve said before, for the AI, allegiance is just a 0-1 switch, normally the game is made just to mess with the player and side with the winner side (you know, the ai will be always op in terms of money and spam units, so in paper the other side to your allegiance will be the prefered choice for the ai)

At least is what i ve notice after countless campaigns around more than a decade.
Hope this helps!

[BastardSword]

Any clan in your faction that neighbors you will pretty much always flip to the other faction and attack you.