Why would one nation have magic and another, none?

Question

Two nations exist on the same planet. One has advanced technology, the other magic. How could this happen?

Assuming that anyone with the right training could use magic and that magic doesn't cause technology to fail or vice versa, explain this.

Answer 1

• Location. Magic-land has some magic mojo aura which allows magic to work. Tech-land hasn't, so magic simply doesn't work there. Tech-land might certainly be keen to research the nature of that magic aura, understand what causes it and replicate the effect, but their scientific understanding might not be advanced enough to do that (yet!).
• Nutrition. Using magic requires to eat certain plants which only grow in the magic-using country and are so abundant there that they are a basic foodsource. Exporting those plants might allow people from the other country to use magic. If you would like to limit that, you might say that people need to eat it continuously for years to gain magic ability and magic-country forbids the exports rigorously to not lose their advantage. Tech-land chemists will likely try to synthesize the active ingredients while tech-land botanists will try to cultivate the plant. Should they ever be successful, magic-land will lose their advantage.
• Genetics. The people from magic-land are from a race which have a gene which allows to use magic. Tech-land people are from a race which has not. Interbreeding between both races might result in people with limited magic ability. Magic ability is likely such a huge evolutionary advantage that you need an explanation why the tech-people race is still around. The magic-gene might either be a recent mutation (evolutionary-speaking) or the two races evolved on separate continents with little to no interaction until recently.
• Cultural taboo. Tech-landers could use magic, but they don't allow it for religious, ethical or political reasons. Considering that magic is quite awesome, there would have to be some oppressive regime to enforce the magic ban and hunt down any magic-users. Such a scenario could be heavily inspired by the medieval period of which hunts where people genuinely believed that everyone could learn to use magic, but those who do are evil and must be executed in the most horrible ways imaginable. Needless to say that this will be a huge source of conflict with magic-land.