1) Benoic and Broceliande fall. You've already scripted the Siege of Ynys Trebes, but I was thinking that Broceliande should either hold out longer or lose in one war, as for now it gets eaten piece by piece which is a bit boring. Armoricans seem pretty much impossible to play anyway so I'm not that fussed about making it easy for them until we have more map space for them.
2) Galahad and Lancelot are in court at Dumnonia. Ban of Benoic can be brought in on it too, but honestly I forsee him dying too quickly for it to be worth it. I don't know what he does in the books, but I'd prefer him to be out of the picture in the event chain.
3) A few flavour events have Benoic mentioned to Arthur/Mordred to remind them of the refugees in their court. These events can basically say that Britons who can't even defend their own lands would be fools to take on the forces of the Franks.
4) Cantuaria and Icenia are formed. I want to put in a few flavour events here, which in Cantauria should allow the Pendragons to "accept" the Frisians presence and gain a valuable ally in exchange for a promise to liberate Frisia. Somewhere down the line of events, if Frisia is liberated, a Frisian exodus event can be fired which removes Frisian culture from Canturia and places it back in Frisia. The rest of the Saxons in Cantuaria should flee immediately, and at that point the Cantian mercenary company should be renamed to something like "The Lost Banners of Cantia" or something fitting. They should then be a free company. In Icenia, the western part of the Kingdom should automatically gain Romano-British culture as Saxons flee, with the rest being flagged a haven of dissent (increased revolt risk, chance of rebels forming Saxons lordships in the county they take). Some time down the line, an Icenian melting pot culture should appear, which should envelop the entire kingdom as Saxons and Britons merge into a more cohesive culture. The Saxon revolts can go, but then there could be a revolt for Icenia which should pull the kingdom out of Pendragon (presumably that'll be who's holding it, if House Cadarn does there shouldn't be a revolt) control much like with Mercia from Anglia or East Anglia/Essex from Mercia.
5) Immediately following the creating of Icenia, Galahad and/or Lancelot should approach Arthur/Mordred about the potential of retaking Benoic. At this point, the ruler should be able to accept or reject them after hearing a short summary of their plan. If accepted, all characters should receive an event declaring the massing of Briton troops on the southern shores to invade Frankland. No war yet, as I want to make at least two county changes into event chains and not direct wars. I've broken each stage down:
a) Brothers of Benoic: Either Lancelot or Galahad gains a mercenary title called the Brothers of Benoic, which should have boats and fairly weak but numerous infantry to indicate that many have travelled over from Benoic in near poverty to try to join the cause. The title should be sworn to Dumnonia. Shortly thereafter, they should go on "raiding" the coast, giving modifiers which means the Franks can pretty much raise no levies and gain no taxes from Armorican cultured provinces. A few months later, they should report back to the King of Dumnonia, remarking that the Frankish hold has been greatly weakened, but that a foothold will be needed to continue. Another decision to continue or stop leads to the next event.
b) The Blockade of the Channel Islands: (this is where I fabricated a claim when I tried to do it without events) should be a big stretch on the dueling engine and I plan to read the Valyrian steel event chain of GoT for further inspiration. In this event, the King of Dumnonia should travel out with the Brothers of Benoic along the coast of Normannia to the Channel Islands to join a growing blockade of the islands. A few events can comment of the current situation, then the boat can reach the islands where it gets caught up in a daring break out at sunrise by the garrison on a series of galleys. The boats grapple each other, the King fights a duel with the captain, and can either die, be forced to flee or take over the ship. If he dies, his heir gets a claim on the county but will have to fight Franks directly for it. If he flees, he gains the claim. If he wins (which should be very likely for Arthur) he then has the ship rowed back, alone to the port, a kind of trojan horse maneuver which should lead to him holding the Lord to ransom. The lord will then surrender, hand the title to the Brothers of Benoic, and join Arthur's court as a traitor to the Franks, recognising the greater might of Britannia. The King of the Franks then gets a massive malus but wont declare war yet.
c) Normannia rises: This should be the first time Dumnonia meets the Franks in open battle. About a year after the Channel Islands fall, the leader of the Brothers of Benoic should come to the King warning him of a buildup of troops and ships in the Kingdom of the Franks. Arthur can then choose to give up the cause, making the Brothers of Benoic independent to face them alone, or to go ahead with their plan to cause a massive rebellion in Normannia. If he does, an event triggered war starts which, if surrendered to, will lose the Channel Islands, and if won will take both Normannian counties. When the war starts new regiments should spawn in those two counties, and if either are Frank cultured they should be returned to Armorican culture. If the war is won, the Brothers of Benoic gain the two counties and the Normannia title, which wont become de jure yet because it'd make Neustria too complicated. On loss, if the Frankish king hasn't created Bretland yet, he will, in an attempt to stop similar rebellions in Broceliande. The ruler of Bretland will come into play later.
d) The Red Winter: The next event, if possible, should be triggered in the winter after Normannia is taken. Reeling from defeat, the Frankish lords should start a campaign to purge the remainder of Neustria of Armoricans wherever they can. During the winter, the King of Dumnonia should receive an event notifying him of massacres and pillaging occuring in the former lordship of Trebes, at which point the Armorican provinces in it should become Frankish. The Brothers of Benoic come forward yet again to express their outrage, and inform the King of a particularly grizzly massacre at Ynys Trebes of Armoricans who tried to escape to there from the countryside. They then put forward a plan to take Ynys Trebes in the following winter, when the Franks are expected to be at their weakest. Arthur can choose to decline this plan or accept, if he declines the situation will stabalise, the Lordship of Normannia will become de jure and part of Dumnonia, but the Armoricans will bear a grudge against him. If he accepts, the Brothers of Benoic will tell him of their plan.
e) The Song of Ynys Trebes: I've always wondered what the point of the bard event was - threatening the bard with having his bones broken always gave a negative effect - so I figured making one bad bard would be a good idea, with this event chain basically experiencing what it's like to be a traveler to a court. In this event, the Brothers of Benoic decide to launch a two pronged attack to recapture the keep from the Frankish governor. Either Galahad or Lancelot (depends who holds the mercenary title, I can't decide who) will disappear before the next winter, citing the capture of something to help the war effort by an Armorican raider in the Mediterranean. Meanwhile, the other brother (or an Armorican character), will lead a small band of men to Ynys Trebes posing as Ostrogothic musicians. A few events will see Arthur and his men see the damage of the winter before, and travel to the burnt out library to pay their respects. After this they should travel to the barracks where the lord of Ynys Trebes is staying, and get a more light hearted event where they have to perform a ballad for them to maintain their cover. Just as Frank begins to suspect their poor grasp of Gothic, he is called away with the men to see a small fleet sighted on the horizon. The ship is led by the Brothers of Benoic, and Arthur and his men must duel the harbour master and his men to stop them intercepting it. If successful, (honestly it'd be a chore coding a failure condition for each duel) the incoming ship should crash into Ynys Trebes, and explode in a torrent of Greek fire. The leader of the Brothers of Benoic should jump out just in time, but be seriously wounded by the flames. The ruler of Ynys Trebes should change to the Brotherhood of Benoic at this point, and the following event should concern finding the former Lord collapsed at the ruined docks, with most of his men dead from the fire. As Armorican soldiers take positions around the town through a breach in the defences and extinguish the flames, Arthur should get the choice to execute him personally with Excalibur or give the deed to the new King of Benoic. After that is done, Arthur surveys the damage, and then crowns the new King, making Benoic de jure, changing Neustria back to Soissons and making Benoic a vassal of Britannia if it's active (de jure vassal regardless). The crowning ceremony should start off the next chain.
f) Anarchy in Bretland: Since Bretland is now cut off from the Franks, the ruler declares independence from the Merovingians, with the lords of the other two counties of Benoic going out with him. Benoic instantly declares war on the two rebels within its de jure domain, and should be able to crush them. Benoic then gets the choice to purge the Franks or to spare them, which should greatly increase respect for Benoic by local rulers but screw them over in the long run. The westernmost county of Bretland should then rise up, and the ruler should ideally be a member of house Trencavel, the rulers of Broceliande if I remember correctly. Arthur can either choose to assist (if which case they'll promise to swear fealty to Benoic as High Lords), or refuse to assist, in which case they'll likely to crushed. By assisting, Arthur gets war declared upon him by the Franks, which aims to be one last push to retake Benoic. At this point the Franks should be unaware that Arthur was the Gothic bard, and will assume that the Ostrogoths have helped their enemy. If Arthur wins the defensive war, the Franks then start attacking the Ostrogoths, which should lead to an early Gothic invasion which should wipe the Franks out slowly (having them linger forever would be boring). Assuming both wars are won, the two Broceliande duchies should be sworn to Benoic and the Franks should then stop trying to invade Armorica forever, believing it to be akin to suicide. Benoic should then rename to Brittany to indicate a union of kingdoms, or Armorica.
g) Consolidation: A few more flavour events to refer to the consolidation of Armoricans, then nothing much else. From here on I'd want to work on a later chain allowing Britannia to restore rome, but Arthur himself might not be able to do it. I lost my trail of thought when I went to get food, so I might edit the above later. The Franks should then get quests showing their collapse, and Arthur should get a mini quest to install the Frisians in Frisia. That should leave the Franks to get swallowed up by the Goths or just sit there with little to do.