1) You are placing vic 3 into the framework of eu5 here, which wasn't what I was getting at, it would have been better if you tried to do this with a game that we know more about. But here goes, let's pretend that EU5 is set in the Victorian period.
2) I have no idea what you mean by 'higher institutions' nor the traitor mechanic, nor how this budget and manpower system would work.
3) How is the cause of the civil war defined exactly?
4) How do I get the War of the Roses casus belli?
Is a religious civil war caused by conversions and 'massacres' (whatever they are in the context of eu5, I have no idea).
What specifically causes this noble war? How does it resolve exactly? What's it trying to be?
5) What causes this civil war? How do you stop this happening in every other country that has slavery? Does it always result in the CSA spawning or local equivalent? If not, how do you stop the CSA spawning in Brazil or the East India Company?
6) How do you kick a ruling family out? How does that relate to the Boshin war? Where is the mechanics for restoring the Emperor? How do you have that system and not have it apply to other states?
7) So, if a nation's control falls, and there is a cultural difference between the people, and there was money going to rebels more than the government, then what? The brother of Jesus pops up?
And you have to take control of the peasant estate? What does that mean?
I took the liberty to edit your answer to add number and limit it to my part. No other changes were made
1) This is Project Caesar's forum. Victoria 3 is two blocks down. I am not assuming Vic 3 mechanics in the slightest. If you do, consider not reading nor replying, for it is off topic. I do not play Victoria 3 anyway so "we" is a false assumption
2) Higher institution: The government, as in, who excert control. The player is the government of his policy (I am not using the term country for it is known that you can have TAG without Location control. Location is defined as the single smallest map entity as per technical term used in DD
Traitor: Generic term for the entity opposed to the government in place
Budget, Manpower: As per DD. Population can be used in the army, this is manpower. Money is money, as in ducats. As per previous Johan post, non landed entities can siphon money, example being the Rebels (as per the common term Rebel, with the classic Red and black Flag)
3) Since entities without Location control have soldiers and money, they are assumed to be able to declare war. In case of a strong rebel / disgruntled estate, triggers would define Locations to immediately switch camp to this new tag and gain Locations under their flag, with a Control (see DD definition) that allow them to tax and levy those Locations. A Civil war is a war. Only triggered by a different set of tag for the sake of denomination, but with same attached game mechanics
4) You do not get "War of the Rose", you get "Pretender rises" (denomination made generic) the pretender being the Ruler of the (civil) war attacking country, defined with a Casus Belli a-propos (likely triggered by low legitimacy from host country Ruler, low Control over rich land, and if applicable, royal bloodline that allows to claim said throne, think Royal Marriage leading to War of succession in EU4, except internal to your Host country)
Religious civil war would have trigger based on two Heretic to each other religion being present and having large enough share of power to consider warring each other, potentially modified by tolerance / laws (we are assuming EU4 tolerance style mechanics for now, I assume Clergy estate would deal with that, but this is a yet to be shown part) but also have the non official religion unhappy, to cause unrest / rebel entity existing
Noble war follows this pattern, this time with the Noble estate being the source of unrest. All of this for now corresponds roughly to the mechanics used by EU 4 to decide rebel type in a province. How it resolve / try to be depends on Noble's demands / civil war Casus Belli. If they want privilege, forcing the country to give them. If they want to put their family on the throne, get rid of your current ruler, and so on. This part, by definition, is flexible
5) Strong slavery present in the country, laws passed by the government to ban slavery. This is bound to cause unrest, creating a rebel entity, and we're back to the usual situation from above, with the Casus Belli "Repeal this Law". Abolishing Slavery as a law is bound to have triggers, but those cannot be clearly defined with our current knowledge. In EU4, there exist a trigger to change the Slave trade goods, but I would not use that here. Slavery ban is bound to be something you do not desire financially, so many countries would not have incentive to use it. As per Johan, Slaves have no rights. Their needs are low, thus making them cheap labor. Unless railroaded, It is potentially possible for no anti slavery movements to happen if the conditions are never right for it to appear. Nothing really prevent the American civil war to not happen in any other country, for it has no reason to be prevented. And it has no reason to be a Civil was only, many non-civil wars were fought to free slaves in others countries
6) Boshin war saw the Tokugawa expulsed from power. I admit this one is likely several civil wars however, but you can see the pattern: unrest (here caused by Burghers getting powerful fast from industrialization / harsh laws they are bound to fight against). Japan is special due to the Emperor / Shogun dichotomy and would delve in a very specific government system gameplay wise. I would see it with a balance of power between both, but we are outside of parameters we can assume, so I'll put it in the "Need to know more" basket. Base mechanic is still Rebel -> War declaration
7) Control is specifically defined in DD. It is how much the state can levy taxes and mens in a given Location, and inversely how much is in the hands of the Estates. Culture are likely to have a system similar to EU 4 of accepted culture / culture group, or close to that, where cultures not tolerated by the government are generating Unrest. And yes, we are back to a new country rising with a Ruler. Due to Rulers not being yet defined fully in Caesar, I can not assume that for instance, an assembly could be a Leader by itself (see the Cromwell case presented by
@Arizal ). And yet. Rebel -> War
Estate have Loyalty, as per DD. If it falls low enough, the unrest it will cause (we know it does) will be what powers the Rebel state. If you make them happy, be it by giving to demands or stomping on them or anything else really raising their loyalty, Unrest will lower, the rebel state will grow weaker, potentially disbanding