Land Division (Spoilers)

Arcadian Empire (90% of the Arcadian continent): Three Grand Orders, Nine Principalities, 18 Grand Duchies, 36 Duchies, 108 Marquisates, thousands of counties, and four tributary kingdoms.

Four Tributary Kingdoms supervised by four Grand Orders (the orders also guarantee the rule of the reigning dynasties on behalf of the emperor):

Orloth: South of the Arcadian Empire; seat of the Blood Rose (Ostria is just a viscounty within Orloth).

Sogard: West of the Arcadian Empire; seat of the Sacred Heart.

Drucia: East of the Arcadian Empire; seat of the Radiant Light.

Nargoz: North of the Arcadian Empire; seat of the Cleansing Wind.

Other mentioned places (just remember them for now, I will give descriptions when the story properly introduces them):

The Wailing Sea, the Chiropteran Dynasty, the Undying Horde.

Ps: Before anyone asks, there is a reason why the emperors don't outright annex the kingdoms. A reason which (spoiler alert) is linked to why Niklas exterminated the eldars. You can guess!