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[TargetSlayer]

I have played three Long Campaigns on Normal - two for the Emperor and one for the Shogunate. In all my campaigns so far I have seen clans change side up to the point where your fame is significant enough where you are given a choice to continue fighting for Emperor/Shogunate or go it alone. I cannot remember any clan changing sides after that point. So it depends. While I usually prefer a solid frontline(s), if you are approaching this mentioned milestone I would be surprised if this clan changes sides. If you do attack him, of course you need to make sure all his Alliances are broken before the attack. Another option is to cause a Revolt, though you will suffer a small penalty on your relations with him (but he won't be around for long anyway).

TS!

[andrewt]

As Saga, I don't think you have much of a choice. You need to get those three very fertile provinces as early as you can. Either backstab them or declare war the moment your alliance's 20 turn extra penalty is over.

[Forward Observer]

Remember that whether a clan is Shogunate or Empire, all are nothing more than petty warlords who are basically looking out for #1. If it either bothers you to turn on an ally, or if it is the fact that said ally may presently be too strong to attack and/or also allied with others even stronger, then simply incite a revolt in their province closest to you. Chances are the rebels will take it, and then you can move in without declaring war. You can eliminate whole clans this way without ever being at war with them.

The downside is that sometimes the rebel army that spawns will be large, they will hole up in the castle, and after defeating them you will find everything quite damaged--which will present you with a substantial repair bill. However, it's still usually cheaper than attempting to build up an extra stack of troops and ships to chance a invasion of a distant enemy province--especially early in the game when your economy is just getting off the ground.

Cheers

P.S. If any of the damaged city structures don't fit your needs, don't hesitate to torch them instead of repairing. Then you can build to suit your particular gameplan on the next turn.

[Trithemius]

Sadly, if you want to bash your friendly neighbours you are pretty much required to be a sneaky jerk! ;)

In my game the Tanegashima got on a boat and went off to capture Kazusa - which made them the most effective of all of my allies really; you could always take a leaf from their book and "emigrate"?

[easytarget]

I've found what I've been doing in FOTS a lot more of is getting on a boat. Since the AI is more navy focused, I have been as well. As a result, I've got a pretty robust navy cruising around, and at the point where I inevitably get bottled in fairly early on by allies, I just continue building my economy, steadily crank out a couple stacks, put'em on a boat, and conduct a rear guard invasion of the opposing side. And I make a point of invading whoever is the strongest, or I suspect going to become the strongest clan among the opposition. Works like a charm.

[Voigtkampf]

Oddly enough, I dropped my focus from the navy entirely. Playing as Choshu, I focused on fortifying my assets, expand only slowly, one province at the time, and build up just enough forces to hold the province from invaders. I usually beat them to a bloody pulp when they assault my castle. Navy upkeep costs a lot of money, so I focused on ishin shishi and inciting rebellions in provinces behind enemy lines. Once my immediate neighbors find themselves with only a couple of provinces under their command, they lose the will to sail around my borders pretty fast.
When playing on harder difficulties, I found that the navy upkeep is better spent on the improvement of my infrastructure, and whereas I did in fact got bombarded few times, it was well worth the cost. Not to mention that once you've expanded you can go and build massive fleets within a blink of an eye and stomp everyone into the ground...Erm, water... Hmpf...

[Trithemius]

Oddly enough, I dropped my focus from the navy entirely. Playing as Choshu, I focused on fortifying my assets, expand only slowly, one province at the time, and build up just enough forces to hold the province from invaders. I usually beat them to a bloody pulp when they assault my castle. Navy upkeep costs a lot of money, so I focused on ishin shishi and inciting rebellions in provinces behind enemy lines. Once my immediate neighbors find themselves with only a couple of provinces under their command, they lose the will to sail around my borders pretty fast.
When playing on harder difficulties, I found that the navy upkeep is better spent on the improvement of my infrastructure, and whereas I did in fact got bombarded few times, it was well worth the cost. Not to mention that once you've expanded you can go and build massive fleets within a blink of an eye and stomp everyone into the ground...Erm, water... Hmpf...

I neglected navy for a while (was going for British trading port so didn't make a lot of other naval centres) and I suffered a lot! I ended up with a lot of exposed coast and repair bills from enemy bombardment. It got particularly hairy at one point with many of my farms and towns being set afire by the angry guns of my (many) enemies - trust me to ignore navy while my enemies focus on it! They even pulled the rear-guard naval invasion trick once or twice themselves, the dastards!