Herbert Spencer notes that traditionally the growth in government revenue has come about because of war (1882)
In his discussion of the origin of the state and the elites which control it, Herbert Spencer (1820-1903) notes that war enabled a king to loot not only those he conquered but also increasingly his own citizens or subjects in order to fund it:
Making him more despotic at the same time that it augments his kingdom, continuance of this process [of fighting wars] increases his ability to enforce contributions, alike from his original subjects and from tributaries; while the necessity for supplies, now to defend his kingdom, now to invade adjacent kingdoms, is ever made the plea for increasing his demands of established kinds and for making new ones.
In his under-appreciated work The Principles of Sociology (1874-1896) Spencer in Book V “Political Institutions” gives a detailed sociological and historical account of how the institutions which compromise the modern state first appeared and grew into the structures he saw around him in the late 19th century. As was common at the time, he realised that the key institutions emerged slowly through a process of violence and power-sharing with other groups. In this chapter on “Revenue” he notes that external conquest has two sides to it - on the one hand the conquest of others and the confiscation of their property increases the revenue of the state, but on the other hand the leader or king also turns upon his own subjects and loots them in turn, either by conscripting them into the army or taxing them to help pay for the army. His rather sad conclusion is “But to the last as at first, and under free governments as under despotic ones, war continues to be the usual reason for imposing new taxes or increasing old ones.”