I don't think that a shortage in Chocolate could incite mass riots. Petrol or Bread, maybe, but not Chocolate.
Why? It's not that important to most people - it's certainly a big selling product, but not addictive enough to cause rioting. Although, I don't know how important chocolate is to Americans, but it certainly wouldn't cause riots in the UK - it's more of a luxury than an essential.
It's a nice treat, but i'm not going to go and petrol bomb a corner shop 'cause they don't have any.