For a well developed high-tech country in a fantasy world, which substance has the highest possibility to be the backbone of their technology?
I mean a physical substance, for example:
- A substance which provides something like nuclear energy.
- A special metal (like in Black panther).
- A herb which cure all diseases?
For my country, trading with another countries is not possible, so I guess something that makes them financially richer has no effect in this circumstance. Also please avoid ideas about something provide immortality. Also I wish to avoid magic in my story as much as possible. Thank you.