'The Savage State'/Polity - <5 Provinces
Military: Lacks discipline, morale and offensive effectiveness, but is more easily defensible. (This can result in large countries having more difficulty completely annihilating a small one entirely)
Diplomacy: Mostly unnoticed on the world stage, low AE and low diplomatic rep.
Economy: higher trade efficiency, but reduced production, taxation. Cheaper build/dev costs.
Innovation: Mired in tradition, institutions spread slowly. Cultures are easily converted, promoted, or exchanged.
Stability: The most stable, you would have to really mess up to get a serious uprising here.
Overall: Polities should focus on marginal gains to sneak out of their small state and move onto the Nation stage. They are often easy to defeat but difficult to destroy. Bandwagoning with a larger power is recommended.

'The Pastoral or Arcadian State'/Nation - 5-50 Provinces
Military: High morale but slightly lowered discipline, recovers quickly from losses. Favors land over sea.
Diplomacy: Mostly unchanged from vanilla.
Economy: unchanged from vanilla
Innovation: Tradition still slows institution spread, but by significantly less than Polities.
Stability: Unchanged from vanilla
Overall: Finally able to act independently, steps should be taken to ensure defense of the realm, handle internal unrest, and press onto a consummate stage. Failure in this stage often is due to lack of allies, impatience, or lack of preparation. Every move for a Nation will be hugely consequential.

'The Consummation of Empire'/Empire - 50-Age Cap # Provinces
Military: first rate military in all forms. Offensive focus. Great bonuses to force limit and manpower.
Diplomacy: Higher AE and Dip Rep as the world stage takes notice of every victory and defeat.
Economy: Focus on production over trade, but higher taxation and overall the strongest economy possible.
Innovation: Pressing the boundaries of the cutting edge of technology, institutions are adopted quickly and technologies are developed faster.
Stability: Though unrest remaisn unchanged, it will be more difficult to get yourself out of a jam by raising stability.
Overall: Empires are the highest and most potent form of state in the game. They will strike out often and potently against any foes they deem necessary. Their only real threats are coalitions of states and other states in the Empire stage. Though some Empires may fall due to mismanagement, in general, most will progress onto the next stage, wielding immense power, prestige, and holding vast swaths of territory.

'Destruction'/Decadence - Age Cap #< Provinces
Military: While maintaining higher discipline, morale has sagged. Both defensiveness and offensive ability is lacking. Status Quo is favored.
Diplomacy: Past its heyday, the world no longer sees this state as a champion of progress, but rather a remnant of the old. Reputation suffers and AE spikes. Corruption seeps through every aspect of society.
Economy: All aspects of the economy suffer significantly. Corruption makes all building projects more expensive.
Innovation: The state remains a bastion for technological development, as its universities and research holdover from the times of glory, but new institutions spread slowly.
Stability: The state will deal with its most challenging, but not insurmountable civil unrest thus far. Internal peace and stability will be this state's primary concern.
Overall: Decadent states are not weak, and will likely still thrash Polities or Nations that it finds problematic. Rising Empires are a threat and internal unrest is the main issue for maintaining the empire. Decadent states are not gone, nor guaranteed collapse, they are merely finished their expansion, and focused on the maintenance of their great empire despite growing vulnerabilities. A Decadent states largest concern will be delaying and preventing the Desolation disaster.

'Desolation'/Collapse - Age Cap #< Provinces
This disaster will progress slowly (on average, for a poorly planning state, 30 years) once an empire enters the decadent stage. A myriad of factors can influence its progress, and many avenues exist to delay or reduce its progress. (High treasuries and stability, for example, and maintenance of one's great power status, can keep this disaster at bay indefinetely. Yes, this may mean you find yourself in a position of needing to beat that upstart rival or lose your position and thus stability. Thucydides strikes again!)
The AI will generally run headlong into this disaster (as intended), but players may find ways to avert it.