This is a record for myself, but given I haven’t been able to find an equivalent readily online: here is a quick guide to the final quests that you unlock based on what form of government you choose when the era changes. I hope this isn’t considered spoiler-y but it’s the sort of guide I would like to have personally.
Guide for Third Era Quests
For autocracies in the 2nd era, at the start of the 3rd era you can choose Absolute Monarchy (AM) or Dictatorship (D). The quests available for this are:
AM: 100000 Sons of St Louis
You are given two field marshals in charge of 6 different soldier/mounted soldier ranks (my personal favourite)
D: Emperor Proclamation
Damage increase of 50% by soldiers for 6 turns, making them effectively invincible – but in my experience, this has never worked or has never made a difference when I’ve accepted the quest. I can’t tell if it’s bugged or if it’s aimed at lower rank soldiers (I’ve tended to use grenadiers or higher from this stage)
For democracies in the 2nd era, at the start of the 3rd era you can choose Constitutional Monarchy (CM) or Republic (R). The quests available for this are:
An territory with a capital under the occupation of another empire (e.g. Lombardia, Saxony, Portugal) becomes a part of your empire. If there are no territories with their own capitals, a territory belonging to another empire becomes part of your empire (e.g. Minsk, Ireland, Silesia)
R: Universal Declaration of Human Rights
All empires (bar the one accepting the quest) forfeit one territory previously annexed (that has it’s own capital), and that territory becomes independent and is given an army sufficient for it’s survival (this means the garrison is filled and the territory is given a field marshal).
The quests each become available in the third era at different stages, with two only available at the very end of the quest tree. Iirc the Emperor Proclamation becomes available very early in this era. I personally prefer the autocracy routes just because you can build medical camps to replenish troops, whereas the democracy routes leave you with a lot of garrisoned troops of a few soldiers.