Very rarely, an individual will be blessed (or cursed, one might very well say) with the gift of magic, perhaps through divine ancestry (or daemonic, given how these things tend to turn out). The magic of the world is not necessarily as powerful as the cannon, and it might be less productive than the steam engine, but being able to bend the energies permeating the aether to your will still makes a very convincing argument for your sake.

There is magic but for balance reasons it's very rare and not excessively powerful. A talented wizard should be comparable to a 6-pounder cannon on the battlefield, only they demand rare cheeses and vintage wines for sustenance. They might be able to heal minor wounds, though, which is nice. There's probably more stuff they might be able to do but GM fiat rules the world here. I think the upper bound on their utility is “what could 10 Guys with proper training and tools do?”.