The vast majority of the money made from war (or the entirety of the money, depending on the war) comes from supplying war materiel. If some actors can figure out how to make money from the subject of the war, fine, but the money is being made from feeding, clothing, and arming the belligerents - so the important thing is their respective bankrolls. US military aid, for example, is not given to Egypt or Israel or the Saudis or Bahrain as dollars, it's given as dollars to US companies to send goods to those countries (to suppress their own populations.) US corporate lobbyists have a multi-billion dollar interest in Bahrain using full military force on peaceful protesters.

edit: There are versions of the theory of "imperial overstretch" that say that empires are forced to expand by the influence of internal elements that are enriched by the process of making war, thus increasing the influence of those elements, forcing more expansion, requiring more taxation and privation from the citizens of the empire, until eventually the entire empire collapses from the strain.