oil is used not only for fuel but for many other things like plastics, some types of clothes, cosmetics, paving roads (don't know how to say that in english) and more. Even if you don't use it for energy you still oil for many other stuff. I don't think that a society has evolved has the one in fallout would live without oil. Also in the end of the quote i made from the fallout bible it says that altought fusion power existed, right before the Great War "few sections of the United States were supplied with fusion power". So, Brother None, the quote doesn't just refer to the portable usage of fusion power in vehicles and armour. It refers to the entire infra-structure of the U.S (there weren't that many Fusion power generators). "Incorporating fusion power into the general US infrastructure begins, but the process is too slow to supply power to the regions that need it."