Charles Mann's 1493 says that when people originally realized just how useful guano was for agricultural fertilizer, they started getting unfree labor to mine i

Charles Mann's 1493 says that when people originally realized just how useful guano was for agricultural fertilizer, they started getting unfree labor to mine it on a massive scale (commonly from islands in the ocean). The paper's reference to Haber-Bosch is because we now instead get most of our fertilizer from atmospheric nitrogen through industrial chemistry. If the demand for guano ever picks up again for some reason, I hope that the "forcing people to work in the mines" part doesn't come back with it.