In non Old Gods start I'd recommend the King of Poland as a start once you are done in Ireland and if you'd like to try a King level title.
Remember before unpausing to do the marrying thing at the start of the game; make sure all your courtiers are married or arranged to be married. It's best to use the arrange marriage button on their character screen so you use other people's courtiers first instead of your own. Arrange a hunting trip and use the remaining gold and piety to invite as many holy men for the ladies or debutantes for the men as you can afford, remembering to arrange marriages through their character screen if possible, matrilineal if your courtier is a woman. At the start those that cost gold cost a lot less to invite and their own dynasties will give your court many courtiers in the future if you take some time to marry them which gives you marriage fodder for your rapidly expanding family tree if needed. In your brother's court is Artur Dmowski, who you should invite to your court and marry to a fertile lady, so you have some couriers with dynastic names that aren't "of Something." He is also a good general. There is also a high Intrigue score fellow you should also invite named something Topor that you should marry to a fertile lady for another interesting dynasty. (that guy helped overthrew the historic Boleslaw through intrigue if I remember correctly.) Somewhere there is someone willing to join your court with the Dynastic name 'of the Opolianie' or something along those lines. Those are the only I remember without 'of Somecity' dynastic names in Poland at the start that you can invite to start pet dynasties before the Dukes and Counts start having children.
Boleslaw Piast the King of Poland starts with really high martial skill and pretty good other skills which makes him a good teacher for his kids. Perhaps more usefully he has a united Kingdom full of weak Dukes. He is also unmarried, but unfortunately Matilda of Spoleto starts married now so no free Italian Duchy bordering Rome anymore. One of the Dukes is his brother, who almost always dies before having children and initially the King is his heir; you can usually marry him to a low fertility wife as well. You border many small Pagan states that you will want to conquer as quickly as possible before the Holy Roman Empire, Sweden, or less likely Denmark take them. It's best to wait until they are involved in other wars as the Baltic states are surprisingly able despite appearances to defeat Poland as they tend to unite against Holy Wars. What I do is wait until the HRE declares Holy War on the Westernmost Baltic Pagan state, then after all the other Slavic pagans join the war and have their armies destroyed by the HRE while it sieges the Westernmost Slavic province I declare Holy War and take the county immediately to the East of it. The HRE will even help as long as your army started the siege. This will cut off the HRE from expanding further into the Baltic states, leaving you to take them at a slightly more leisurely pace. Poland does not start with a coastline so that gives you even more reason to need to take those provinces. Just be careful the Pagans don't form the Kingdom of Pomerania, that one's a pain in the ass that I've seen take and defend Brandenburg from the HRE. After I take one of the coastal Duchies I usually find a distant relative with kids or at least a talented young economist I can marry to a fertile/genius wife and put him in charge of a single Duchy level Republic so I can get 100+ free galleys from them which is well worth the rebellion/faction risks if you have a lot of troops and not many boats. Then you can work your way through Lithuania to form the Wendish Empire, as long as the HRE hasn't taken too much territory required in the SouthWest. Then you go up the coast before Orthodox Russian states or Sweden take Finland. If the Pope calls a Crusade for Jerusalem after you have coastline you'll have a navy to carry your forces somewhere away from the Muslim doomstacks. Attacking distant points will have them split their forces and allow the HRE's own doomstack do their thing. HRE tends to get beaten anyways but puts up a better fight this way. If you have hired any holy orders you have a good chance of being the highest scorer in the Crusade.
After all the Pagan states are absorbed, you'll probably have to resort to the usual tactics of marrying so your Heir inherit foreign lands or making false claims on weak powers. HRE is usually too strong to steal provinces from so I usually try to ally with them. Cumania and other Tengri states seems to do pretty well usually, so if you border them you can take land from them on occasion with Holy Wars though more easily if they are distracted by other wars. Hungary is a much better target; I can usually take it over by marriage and murder to send the inheritance to my oldest son. Russian states are also a good target, especially if they are splintered. If one forms the Kingdom of Rus, you could be in trouble. The Empire of Russia being formed would mean you are sandwiched between two Empires. In both cases they are excellent allies, especially if their ruler is the same religion as yours.
Eventually the Mongol hordes show up and just ruin the AI controlled powers in the East. Oh, and there are two of them. The only time the AI has managed to stop the hordes in my games without my help was when the HRE for some reason intervened several times on behalf of an Eastern ally and killed most if not all of the no attrition hordes. I think because in that game most of the Russian Duchies had mysteriously been converted to Catholicism while Hungary was Orthodox somehow, the reverse of the usual. Usually as Poland/Wendish Empire you will have to defeat the Mongol hordes yourself before they have so many territory and levies that they can fight several wars at once even without their original doomstacks. I tend to send my councilor to the Mongol court so they usually go around whatever Eastern holdings I have, while joining as many wars as I'm able to against them. The goal is to destroy their hordes. Each one you can destroy is a major victory even if you lose the war and your ally is made landless.
Author
Topic: Crusader Kings 2 is released. (Read 2124543 times)