The Roman Empire, the French monarchy, the Chinese imperial dynasty, and the British monarchy were all built (and sustained) largely on salt production, salt taxes, and salt exportation. Kurlansky makes clear throughout the book that while most people may never think of salt outside of its context as a seasoning, it has been a tool—and sometimes a weapon—wielded by industry titans, despots, and corrupt governments. An empire is founded on the strength of its economy, military might, and the degree to which it can maintain the support of its people. When a nation went to war, its government often raised the salt tax to increase revenue. In this way, the literal war effort was fueled by salt. Without salt, an army could not feed its livestock, transport enough food to feed its soldiers, or maintain morale. If the army languished, the expansion of an empire halted, or the empire could be assailed by stronger forces with greater resources. 

The high demand for salt allowed governments to impose oppressive salt taxes on people who could barely afford them. Kurlansky shows that whatever can be exploited eventually will be, and salt has not been an exception.