tanks are old world relics that can be found all over the continent of Laurentia. They are restored and modified to properly work with the fuel available. Most often they end in charge of warlords but also they can be under the power of free men capable of maintenance of their war vehicle. This means they have to have knowledge on engineering, mechanics and on top of everything have a crew with high magic prowess to make the best out of the black soil fuel that works with this mysterious energy from those cursed
Funnily enough the age of discovery of this old technology brought a moment of tense peace between various factions of Laurentia, since so many chiefs were afraid of confrontation, not knowing the real power and potential of these different vehicles :)