Jared Diamond says that some cultures kicked ass because of access to storable food, work animals, and iso-climatic paths of expansion. Let's extend that environmental determinism to encompass available drugs.
Just like food, the storability of drugs determines prevalence. For each culture, we can place their storable drugs on a spectrum that ranges from stimulants to depressants. The cultures that have more stimulating storable drugs will dominate the cultures that have more depressing drugs.
All hail the rise of the Modafinil Culture?