It is actually really simple to start as a single county and it is again quite easy to gradually and sometimes rapidly grow to be an enormous empire within a century.If you do things right even mighty Fatimids are of no real threat and it is also possible to start as a jerusalem count and work your way up to being King of Jerusalem,and even to become emperor of Persia,forming Persian Empire conquering whole of Persia,Azerbaijan,Syria,Anatolia,Arabian Peninsula,Egypt.And then it is possbile to crush Ilkhanate to dust and reduce them to a single vilayet/county and humiliate them all you like
Ok from my several campaign experiences here are some detailed hints,if you abide by them you can be rich and militaristically powerful as well as you can manage easily huge empires.
1- At the start of the game and actually always you need a decent council.In my opinion,at the start of the game especially most important council member you need to get is a decent Marshal.Secondly you will need a good Chancellor because you will need use your Chancellor to fabricate claims on other counties and duchies if need be.When acquiring council members you need to opt to get someone with a skill of 20 at least.At the start of the game you have 40 gold that means by sending gift option of 20 gold if need be you can use 40 gold to get two council members.One of them should be a good Marshal with a martial skill of at least 20(because with train troops option it will enlarge your default troop size) and again you need a Chancellor with a skill of 20 diplomacy.What you need to do is open up search character screen,and search for someone same religion as you(because there is no way to get characters from other religions to your court),check imprisoned as no for search criteria.When the list comes up you click on the highest martial skill to search for a marshall.Important facts here are look at their status if they have a title meaning if listed characters are counts,or dukes or bishops they won't accept your offer.So you can get other council members chancellors,spymasters,stewards or courtiers.
Another hint here if the character is married that is better.Because if he doesn't accept the offer to join your court his wife may.Click on the characters portrait and check the pluses and minuses below.You need at least one "+" on what says opinion of that characters liege.And you need like 2 or 3 "+" for opinion of you.That character's opinion of his liege is the greatest factor determining whether he will join your court or not.Don't even bother with characters with several "-" on their opinion of their liege they will never come to your court.So search the list from top to bottom trying to get a marshall and councillor.Use all your 40 gold for gift if need be.
Once your new marshall and new chancellor arrives at your court immediately set your new marshall to train troops and also send your new chancellor to fabricate claims to the target county that you want to conquer.
1- As you know,when you start as a single county generally you have a few vassals.A major and a bishop or perphaps up to 4 vassals in total majors and bishops.Regardless,these vassals are your first targets to supremacy.In order to militaristically overpower another County you need the FULL levies of those bishop and major vassals since it makes a huge difference,you need to hold the bishopric and city title yourself.Also you will get the FULL taxes of the bishop and the major.And keep in mind don't spend your money on ANYTHING.Save it you will require at least 75 gold for hiring a mercenary band of 1500 strong.Mind you that probably hiring a mercenary band to conquer your first county is an overkill because you will outnumber and crush his army with yours since he will come to battle with troops of a single county whilst you have the troops of a county a bishopric and a city.
2- Supposing that you have a bishop and a major vassal.You will need 10 piety to imprison each one of them.And 10 piety to banish them.So basically you need 40 piety total in order to confiscate all their titles and their gold which is really a great help and a good amount at the beginning of the game.You can also revoke their titles after imprisoning them.But it is most likely that provided that you start in an early scenario like 1066 or 1080,Kingdom or Empire you are part of have not passed Limited Crown Authority Law which allows title revokation.And if you are part of HRE there is at least one civil war which can last several years before the law is passed and title revocation is allowed.Also other than this forget about title revokation banishment is better because you gain very good amount of gold.
Patiently wait to gather 40 piety which takes up to 8 years or the duration could be lot less if you ruler have traits like Humble or Zealous.Also there are certain events which gives you between 5-25 piety they get triggered during hunts and other events,some are random.At the meantime remember to save your money and don't spend for anything.Once you have 40 piety imprison them and banish them confiscating all their titles.At this point you will have 0 vassals.You will get tyranny penalty from your courtiers and other rulers as well but don't mind that.
Now presuming that you have used your chancellor to fabricate a strong claim on the target county and acquired the strong claim on the said county,just declare war on him by using this casus belli.Save at this point.Like I said earlier hiring mercenaries could be overkill but if you want do so.When they emerge at your county at once merge them with your own troops otherwise they will loose the battle since they start with near to 0 morale.With your own troops you will outnumber them greatly.And numbers matter a lot in this game.When they raise their own army attack and destroy them.
Here is a detail.Since your army will outnumber them they may tend to run away facing an open battle.What you need to do is divide your troops and set new troop number to something which will equal theirs.Send this detachment first to attack them.And when they are engaged in battle,immediately send rest of your force,you will beat them.After you see Battle won screen immediately pause and see where their defeated troops go pursue them until they are totally destroyed and then go and siege their county.At this point probably they will have like 220-300 defenders.Just use assault option whenever you can.Just make sure that after an assault had ended wait until your sieging army's morale get fully replenished and then assault again.
You may loose some amount of troops but it doesn't matter supposing you hired mercenaries you need to end the battle quickly since their upkeep will put a monthly negative on your income.If you haven't hired mercenaries you may just wait the siege to end by itself.Eventually you will win.During the war when you have beaten their army and having conquered their county capital you may get a peace offer from your target check the conditions and compare them in the diplomacy screen with "enforce demands" option if they are the same accept the peaceoffer.Now you have gained your first county.
Remember here you need to use this system until your demesne size is full.I mean you need to gather all strength to yourself by banishing vassals be that bishoprics,cities baronies,counties whatever.And once your demesne size is full.You will give your bishoprics or cities to someone else holding onto county titles.
3- Now you hold 2 counties,a bishopric and a city.Remember once you gain a county within a duchy,in the intirgue screen there will be a new plot available called fabricate a claim on duchy X.You need to have at least 3 backers and if I remember correctly plot power of 80.Try and see if you can fabricate a claim on a duchy if you can,with help of mercenaries.You can declare war on the duke and become a duke if you win.Supposing that you win,he will become your vassal as a count.And you wont be able to revoke his title since you have won,you have made a peace treaty which doesn't allow revokation.It doesn't matter banish the ex-duke and confiscate all his titles.
Keep in mind,here having a strong claim on the duchy is quite important.Because the gain is greater when you win otherwise you will fight the duke for a single county and will face the same army for a smaller gain.
4- A.I will tell you a bit about managing vassals.At the point of game when you have become a duke,when your demesne is full but not with counties,but you hold bishopric titles and city titles.At this point you need to gain a vassal.Actually two vassals.One will be a major and the other will be a bishop.Since you have banished many people and confiscated their titles,you will be hated in your realm as a tyrant.But here is the good thing.You can find people who are unaware of your tyranny.Use the search characters again.Find two people who have positive opinion of you.Invite them to your court.Now give all your cities to one of them and give all your bishoprics to one of them.And they will love you for it they will be your loyal lackeys.
B.Also whenever you can every 5 years immediately pass a law.Your initial priorities should be harsh city tax,harsh feudal tax etc. when passing the law set everything to maximum.Don't worry about getting negative opinion modifiers it's always managable.You will always be "feeding" your vassals with new titles (up to a point) and when they are beyond redemption you will kill them and set new vassals.Eventually you will get very good tax and good levy size.You will be easily able to pass the laws without opposition since at this point you will have two loyal vassals and your own vote will carry more weight than theirs anyway.Pass laws whenever you can every 5 years.Assasinate the negative opinion opposers to the law and bribe the new title holders if need be.
C. Planning your expansion is very important.System you should use should be like this.Conquer counties of an another duchy.When you control more than 50 of duchy's de jure counties.Usurp the title from the enemy Duke.Remember as a duke you can hold as many Duke titles as you please without any opinion penalty.Always hold the Duke titles yourself as a Duke.At this point your demesne is full.So you will need to create a count.Decide who this person will be prior to conquering the first county of the duchy.This person MUST be a kinsman.Remember to send gift to him before having conquered the county because if you do it afterwards and a certain period of time had passed,cost to send gift to him will be relatively higher.You will give the county to this person as well as when you conquer the other counties of the duchy you will also give those counties to him.Basically he will be a duke without a title he will have -20 opinion on you because he will want the duchy title but it doesn't matter since you've fed him enough by granting him counties.
After 10 years,since boost to your vassal's opinion modifiers by you having granted him several counties will go away,that kinsman vassal of yours will likely cause trouble.At this point if he has negative opinion of you.He may start a faction,he will be paying less taxes and will provide less levies.Again at this point you may decide that he has outlived his usefullness and you have two options here :
1- Good old imprisonment and banishment.After doing this you need a kinsman of yours which lives abroad come to your court so he won't be getting the tyranny penalty,when he arrives at your court just use send gift and give all titles confiscated by you to your new loyal kinsman.And voila you have a loyal vassal with 100 opinion of you for another 10 years.
2- Second option is,provided that your ungrateful kinsman vassal has a heir.You can assasinate him and his heir will become count,immediately use send gift and award an honorary title.With this method you can't get a very high opinioned vassal but you will gain at least a more loyal vassal,with an opinion of you being much higher than his dead predecessor.
There are really lots of details and tactics hope this helps.If I can I will try to explain more later.
