Some basic concepts you can carry forward from EU4. Stability, war exhaustion, manpower, attrition, claims on foreign territory to declare war, etc. For the new features and changes in 1.2, here’s an 8-minute video:
There are three main categories of government: Tribe, Monarchy, and Republic. They each play pretty differently and they have variations within those categories.
I started out playing Tribes and they’re still my favorite, I can give a very high level overview from a Settled Tribe (as opposed to Migratory, which have other mechanics a well) perspective.
Tribes have Clan Chiefs with their own retinues that they pay for directly (free troops!). They also have a Centralization stat that indicates how settled the are. The more centralized they are the weaker the clan chiefs and their retinues are.
I like Tribes because the game plays in distinct stages. The early game is about getting more centralized which is mostly accomplished by passing the appropriate laws (done so via the Government | Laws screen). You also want to found your first city as that’s where you’ll accumulate Citizens which provide all your research, you really won’t be teching up at all until later.
To reform out of a Tribe, you’ll need to get your Centralization up and various laws passed. You’ll also need a city when 50 Civilization rating, which can be boosted by doing the urban planning action. Once you have it, you can then reform into a monarchy or a republic based on which laws you have selected.
The next stage is modernizing your nation. You want to start centralizing population into your city or cities and have your Tribesmen pops promote into more useful pop types. There’s various buildings and governor policies that can affect this. As the number of Citizens increases, your tech will finally start moving and you’ll get to see how that system works.
At that point you reform your government and you’re at the stage where more civilized nations start out at and you’re ready for more ambitious goals of regional conquest . You can conquer all you want as a tribe and I do so, but you’ll be absorbing more uncivilized peoples and lands which can slow down your goals of modernizing. At this point you’ll also be dealing with the issues of whichever form of government you went with. Republics have to deal with the Senate and political parties, monarchies have to deal with pretenders, succession crises, etc.
In any case, a tribe game starts out slow and if you play one you’ll likely be playing at speed 5 for stretches. What I liked about it was mechanics were kind of introduced over time, which gave me time to absorb how they worked while I fiddled with the various buttons and dials to see what does what.
I typed this out on my phone, apologies for any egregious typos or autocorrect shenanigans.