The Life of Ivar the Boneless
This is designed as a guide tor players who start in 867 AD as Ivar the Boneless and wish to establish a large realm in Britannia that is relatively stable. When you start off in 867, you are at war with both Northumbria/Northumberland and East Anglia. Your brother and ally Halfdan Whiteshirt rules Jorvik, a single county holding. My first recommendation is to immediately begin taking the Northumberland holdings, so that when you are victorious you can claim the Northumbrian territory instead of your brother Halfdan. If Halfdan does acquire these holdings, it's no real problem: you can always use the subjugation casus belli against him, although each ruler you have can only use the subjugation casus belli against another pagan ruler once in his lifetime, and you may want to hold onto it to use against your brother Sigurdr Snake-in-the-eye, upon his prepared invasion of England (if he wins, he will take over Mercia, which if you subjugate can be very handy indeed). After this send your army to take the counties in East Anglia, and you are set to begin the next phase of conquest.
A note as to the war itself and battle that may take place: your forces are generally superior to those of the Catholics in Britannia, even though pretty much all the Catholic rulers will ally against you in any war you undertake. You will usually have better generals, since you have Ivar the Boneless himself, and can train your children to be Brilliant Strategists. Your numbers are usually superior as well, so as long as your forces are kept together, your forces are well led, and you seek favorable engagements you ahould have no problem. Massing your forces to take out smaller contingents of the enemy is the best way of doing this, especially if they are significantly smaller or on unfavourable terrain.
After winning these conflicts, it's time to begin conquering the rest of Britannia. I would suggest starting by picking off the counties of Strathclyde and Scotland, as well as the Welsh counties, in order to avoid Trucebreaker penalty and prestige loss (which probably doesn't matter all too much, but prestige is handy and you need a reserve built up in order to break truces consistently). Conquering Ireland should take no time at all, and will provide you with even more troops and land. I usually attack Irish counties when I still have truces with Strathclyde, Scotland, and the Welsh petty kingdoms, so that I am constantly acquiring new territory without prestige loss of Trucebreaker. Upon conquering a county, I will summon three holy men to my court, losing little prestige to do so, and assign them the holdings of said county. In this way I get Norse Pagan rulers to preside over the territory without having to spend money.
When considering forming or siezing titles, I would highly recommend only having one of the highest title around; if you are a petty king still, I would not create any ducal level titles, and if I became king of Scotland or Ireland I would not create or take any other king level holdings. This is due to the Gavelkind succession curse that Norse Pagans suffer from, as upon your death your realm will be divided. The most difficult part of this whole process is the dilemma of what happens after Ivar dies, which I shall treat with more detail towards the end of this essay.
If you are relatively free from misfortune, Ivar should live through these conquests, allowing you to expand exponentially. If you have the misfortune to lose Ivar through age or battle early on, you could quite possibly be screwed; in my one game where I lost Ivar early on, during the initial war with the Northumbrians and the East Anglians, he was rendered incapable by having his skull crushed by an Irishman at the battle of Kildare, and Ivar's useless son Sigrtyrgg (who is responsible for my three or four games as the af Ivar family going south) took over, and through his incompetence I had to convert to Catholicism just to survive the Catholic counteroffensive. Although Ivar has the strong trait, making him substantially healthier (he has usually lived into his 80s when he hasn't died prematurely) he starts off as a 50 year old, and his exposure in battle renders him vulnerable to being wounded, maimed, or killed. You don't have to use Ivar in battle, but he is your best general around, all the others you start off with having only 16 martial max approximately, while Ivar has something like 22 martial approximately. Nevertheless, keep a close eye on Ivar, because his death is the ticking time bomb that can undo all of your hard work. In my best game as the af Ivars, I had conquered or vassalized all of Britannia except for the southen Irish provinces and the petty kingdoms of Mercia and Wessex (the Norse Pagan ruler of Brittany had conquered Gwynedd, but they were non hostile to me and I figured I could easily pick up that county later on). I was still in the process of conquest as Ivar, and I was Norse Pagan still because I wanted to carve up what little remained of Catholic Britannia. Then Ivar the Boneless died. His ineffectual son Sigrtyrgg, who didn't have the decency to die before his father did, became king of Scotland and ruler of most of Britannia. Within the psace of days a full on civil war had begun, pushing the claim of one of Ivars other sons. I kept playing, but as of approximately 15 years later or so, maybe longer, my character was no longer king of Scotland, the realm was torn apart by constant civil wars, and Norse Scotland was being carved up by the rising powers of Connacht and Mercia (Mercia was actually able to form the kingdom of England at this time). In the span of a few short decades, the great power of Norse Pagan Scotland had dissolved into nothingness, barely clinging onto northern Scotland. All of the territories of Ireland and all those in Britain south of the Antonine Wall were liberated, leaving a shell of Norse Scotland's former power and glory. In regards to this, I have several suggestions to make regarding future stability of the empire.
1. If you have a large demesne (most of Britannia under your control), you should probably switch to Catholicism. Although I wanted to play through the whole game as Norse Pagan and have yet to try converting to Catholicism as a Norse ruler, it grants a certain level of stability to the realm that just isn't possible with the systems of Norse Gavelkind succession and the inability to raise crown law any higher than low (it should be at Medium crown authority, to prevent vassals from waging war on one another and thereby upsetting the balance of power within the realm. It also allows you to revoke the titles of traitors without an opinion penalty, I believe). To convert to Catholicism you just need to have a concubine or wife who is of that faith. I assume this works with women of other religions, but I haven't seen it yet myself. The major problem with this playing as Ivar is that he is already old, and even if you do covert you have to wait at least 10 years after acquiring a kingly title to change any of the succession laws in your kingdom. Theoretically you could convert to a Christian religion in order to stabilize your realm, only to have Ivar die before he could change to succession laws to something other than the awful Gavelkind system. At the very least, however, converting to Catholicism will prevent any remaining Catholic rulers in Britannia from waging Holy Wars on you for entire duchies at a time. This will keep external threats at bay, even if you are still vulnerable to internal ones.
2. You should consider changing the succession laws to Agnatic succession, especially if still playing as Pagan. While this is not nearly as critical if playing as a converted Norse ruler, when playing as a Pagan you need to have as few rival claimants to the throne as possible. This is entirely due to the Gavelkind system of succession, and the dire possibility of endless civil wars that I have seen tear through my realm in a horrifying display of Murphy's Law. By limiting rival claimants to the throne, you reduce this possibility, although you still have to contend with peasant uprisings, independance movements, nobles fighting for lowered crown authority, etc. Your hands will be full, and you need any breaks you can catch.
3. Do not take concubines unless trying to convert/have as few children as possible if still pagan. Related to point number 2, you need to limit rival claimants to the throne as much as possible when playing Pagan, to a significantly lesser degree when playing as Catholic. Although concubines grant you monthly prestige gain, as Ivar you will be conquering so much that it will be virtually impossible to ever exhaust your prestige reserves, unless you invite a ridiculous number of holy men to your court. Having fewer childen should stabilise your realm, although in all reality even a single extra title claimant could prove to be your undoing. Having a Catholic concubine is useful for converting, but after that I would put her to the side in order to limit having any additional children.
All in all, playing as Norse Pagans the greatest challenge you will encounter will be succession crisis. The great strength of playing Norse Pagan is their sheer military prowess and ability to conquer new lands quickly, while their weakness is in holding onto their territorial holdings, which becomes exponentially more difficult the more lands you rule over. As sad as I am to say it, if you are successful playing as Norse Pagan there will eventually come a time when it is time to convert, or let your empire slip out of your fingers. Hope this introductory guide is useful for anyone playing as Ivar the Boneless, or as a Norse Pagan ruler in general.
Also he fell in love with a girl named Nicole.