In my campaign world, the way I did it was have this really big, powerful and advanced (relatively speaking) nation, ruled by a king and governed by an intolerant religious order. The order follows their one true god and have decreed arcane magic to be evil, vile and thus illegal. That is how it started anyway. Today, the result of centuries of propaganda, by the order, of painting arcane spellcasters as necromancers and witches who steal babies and cast spells requiring human sacrifices, is essentially that the general population hates and fears arcane spellcasters.
When one is found (pretty rare these days) they can be lunched, stoned, hunted and exiled ... if they are lucky. If they are unlucky they are imprisoned, tortured and executed. Draw upon the horrors dealt to men and women in the dark middle ages and you get the idea
There is still magic in the nation but the church has the monopoly on it and it is rarely shared with anyone outside the church. This effectively makes the nation a low-magic area.
The rest of the world is not quite as bad as that but still remains low-magic, in the sense, that studying and learning magic takes a lot of devotion, intellect and is very expensive.
That is my two-cents. Hope it was helpful in some way.