Damn, I couldn't find this thread anywhere, but I have posted a thread on the issue of saltpeter. I knew the chemistry education would come in useful somewhere
Yeah, saltpeter is mined and used to manufacture gunpowder. The other components of gunpowder, charcoal and sulphur are very common and thus would not need to be special resources in themselves...
It looks like Provost Harrison was right about the saltpeter as a strategic resource for gunpowder (which, like bronze, is manufactured, not natural). If you require more proof, see:
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