The Assyrian empire has gone into history as a ruthless military power. Consequently, one is easily led to think that it expanded primarily by means of arms and unrestrained aggression. As we have seen, however, the truth is somewhat different. In reality, the expansion of Assyria took place less dramatically, almost imperceptibly, through political deals with foreign rulers (or would-be rulers) seeking military aid, peace or other favours from the Assyrian king. By signing a treaty with the Assyrian emperor, these rulers traded off their national independence for Assyrian vassalage. And once Assyria's overlordship had been formally established, there was no escaping from it. Broken treaties were severely punished; sooner or later Assyrian armies poured into the rebel country, which was utterly destroyed and annexed to Assyria.
No doubt the Assyrian kings preferred 'expansion by treaties' to expansion by aggression. Waging war was costly and time-consuming, and wasted the resources of both Assyria and the target country. By contrast, the advantages of acquiring vassals and allies by diplomacy were self-evident. Shrewdly drawn-up treaties added the vassal's troops to the imperial army, channeled a significant portion of his wealth to the imperial treasury, and subjected his country to a process of gradual Assyrianization, sure to make total annexation so much easier at a later stage - all this for little or no extra cost. What more could even a greedy emperor have hoped for?
On the other hand, broken treaties also worked to Assyria's advantage. The brutal military measures needed to annex a country were now conveniently sanctioned by the curses written in the treaties. On the ideological level, every broken treaty was a sin against the god Aššur, and thus the invading Assyrian army could be portrayed as the 'sword of Aššur' which the perfidious vassal himself had called upon his land.[[8]]
8 Compare ABL 292: 5ff, a letter of Assurbanipal to his general Bel-ibni dating from the final phase of the Šamaš-šumu-ukin rebellion: "You know that through the iron sword of Aššur and my gods you destroyed that country by fire, (so) that the country backed down and could be subjugated, and you returned it to my control."
Simo Parpola
Simo Parpola, 'Expansion through Treaties', Neo-Assyrian Treaties and Loyalty Oaths, SAA 2. Original publication: Helsinki, Helsinki University Press, 1988; online contents: SAAo/SAA02 Project, a sub-project of MOCCI, 2020 [http://oracc.org/saao/saa02/treatiesasinstrumentsofimperialism/expansionthroughtreaties/]