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.
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.