Arcane magic comes from a wide variety of sources, however only one source is sanctioned by the Dragon-Kings. The only form of allowed magic is draconic in origin, either from a pact with one of the Dragon-Kings, from the user’s own draconic bloodline, or from studying the magical tomes possessed by the Dragon-Kings.
Despite this, arcane magic can be harnessed through other means. For example, making pacts with entities from other planes (entities the Dragon-Kings fervently deny the existence of), or finding ancient spell books from pre-draconic civilisations. Some sorcerers may even gain power from strange Wild Magic Events, but open displays of magic from these events are banned by most Dragon-Kings.
Each Dragon-King has slightly differing rules on what magic is banned and what magic is allowed, but its generally wise to avoid practicing any non-draconic magic in plain sight.
Divine Magic does not officially exist, and only a select few even know of the gods that provide it. The only official religions are those that worship the Dragon-Kings, but no divine magic is drawn through their worship. There are rumours, however, of forgotten gods, and those who harness their power.
Divine Magic does not provide any particular advantage over Arcane Magic, as through the correct use of Arcane spells, even magical healing can be simulated. However, it is much easier to use Divine Magic for these sorts of effects.
Runesteel is a rare and powerful metal from another plane, which has the unique ability to grant magical power to runes written on it. It is very rare, and highly sought after, but often using the rune destroys it, or renders it unusable for a long time. Most of the runes draw power from the spirit realm, and as a result its magic is more druidic in nature.
Many weapons are also forged out of Runesteel, including primitive guns. These guns use the runes to launch ordinary bullets, but you could craft the bullets out of Runesteel and inscribe them to get more power.