Leyrann
Deity
-stop making iron being rared than diamond
In my opinion strategic resources just need a re-think:
Horses: Ever heard of breeding? One resource of horses should be enough for your entire empire no matter what.
Iron: Literally the most abundant element in the earth's crust after oxygen (from oxides), silicon (from silicates) and aluminium, easy to process.
Aluminium: Literally the most abundant element in the earth's crust after oxygen and silicon, and before iron, easy to process once you have the required technology.
And the gunpowder resources ("niter") aren't too rare either... Arguably sulfur is the rarest (seriously, animal droppings are not rare, certainly if you have domesticated animals, so that's where you got your saltpeter) and well, sulfur is still more common than, say, nickel, zinc or copper. Let alone tin which is waaaaaaay down there in abundancy.
So yeah, coal, oil and uranium are the only strategic resources that make sense...