Have you given thought to how international law might shape your world? Even having notes on which nations subscribe to a body of international law standards can be a fun way to add depth to the political landscape.
Legal systems can be interesting (no really!) Americans and Britons are used to a common law, where legal precedents form the basis for future rulings, but there are other forms as well - the Roman system of civil law, and the Muslim system of Sharia law also exist.
In my setting, a fallen empire's legal system formed the basis for a loose international treaty for the kingdoms that arose in its place - thus, the Pandect, a series of codes and standards to which today's kingdoms and republics all either flout, follow, or attempt to follow in various ways.
In the main branch of my universe, I used the UN as the center of a world government post magical quasi-apocalypse. Never needed to get too deep into details, but the laws reusing regarding use of magic as weaponry against other nations was covered "on screen", as was the basic human rights charter.
But the main universe is set up for TTRPG, and has had changes here and there, including a few years as a monarchy on earth under the reincarnation of King Arthur.
In the branch I use for most of my writing, things are a little less explosive, and there's no world unification. There is still a UN, and a more powerful world court and legal cooperation via interpol.
However, there's also a separate set of laws called The Pact, which was made between the gods, the living, and all the major spiritual powers. The exact details vary by universe branch, but the two biggest ones cover when and how gods can intervene in the material plane, and when and how spirits can manifest.
The key difference in the Pact between the two main branches deals with the soul. In the TTRPG version, souls can still be bought, sold, traded, etc, but there's limits involved that prevent eternal consequences. In the literary branch, souls are inviolate for the most part. Interference with the natural movement and cycles of the soul are harshly punished by all signatories of the Pact. It's at the center of the main character's stories since he's a necromancer.
Again, not everything has happened "on screen", but I've got scribbled notes and a backlog of brain notes that are moderately developed.
Not enough necromancer protags in fiction. Off the top of my head, The Laundry Files? Is that about it?
Got to love a good King Arthur reinsert. I have one, but more as a sort of Arthas Menethil "back from hell, changed" sort of thing to keep in my pocket in case I need a bigger baddie one day.
There's more than you'd think, but the only other one that sells decently is Johannes Cabal. And it is a great series
My group actually played the return of Arthur. From his initial discovery of his previous life, meeting Gwynevere, Lancelot, and Gawain, then questing after Excalibur. He ended up fighting off a dimensional BBEG, saving the world and being named king until I did a reset of canon because it turns out that a monarchy on a world scale turns boring until and unless the characters go power hungry lol.
I have always loved the idea that in the afterlife there is simply more bureaucracy and legalese. It just seems so human to have even more laws after death.
Not so much a legal code as a series of trade agreements and stipulations for said commerce.
The Cartric Republic, formerly the Holy Realms of the Cledic State, require a series of conditions to be met in order to truly benefit from their economic model and global trade connections. While certain quotas and other mundane numeric goalposts must be reached, the widest in scope and most heavily criticized requirement is the banning of magic in the nation that wishes to trade.
The HRCS was a colonial theocracy, spreading the gospel of the true creator and laying low those that worshipped heathen entities, all to save the souls of humanity from the temptations of darkness (I feel like I've heard this before...). The use of earthly magics was a tell-tale sign of said worship, and the magic frequently attracted or birthed shadowy corruptions that would periodically plague the land.
The HRCS was eventually transformed into a republic, but the resentment of magic was still deeply ingrained in the culture and government. The regions of the world they hadn't taken over outright would often capitulate for the lucrative technology that came from these anti-magic zealots, and often adopted many facets of Cartric/Cledic culture.
Exceptions have certainly been made, such as for the viceroyalties of Varhoste, as their deep mineral deposits are a great resource for the industrial Cartref, but the Varhoster mining infrastructure relies on stone weaving, an ancient magic practice. The deeply religious practice of stone weaving has since been restricted, requiring a license to use (for industrial and military use only), causing some discontent.
I admire this for how the details have a reflection in the larger themes at play, but it all manages to sound fairly organic in how it plays out. This one's my fav.
At least for magic, most nations on Irdas defer to the standards set by the Arcane Council of Everstone. Everstone is a city-state run by mages and they have a council of wizards, each a master at their school and considered the greatest of their time. These wizards meet together at least once per year and update their stances on emerging magical theory. It is kind of like an ethics board. Many nations across the world have taken to adopting their stances when dealing with the publiv practice of magic even though the Council has no official legal power.