A logical fallacy is assuming going to school makes you intelligent, when it only serves to make you educated. Scholars don't advise politicians on how to run military campaigns, Generals do, given that I would have to say for you to casually write this man off as having no knowledge of what he speaks of through experience is rather laughable. You know when you assume you only make an ass out of you and me, correct? The gain/profit from the Christian Crusades was to reclaim the sacred holy land in Jersualem from Muslims. You reclaim the land, force the opposition out and who stands to argue with your power and stand in your way? Not many, hence easy proliferation in wealth from the region. You understand politics back then works like today, right? If the social reasoning i.e general population under which you rule/advocate power wants you to do something, you do it to stay in power and profit. You speak of other variables that allow war's to be waged which is the basis of how they are given opportunity in the first place and why so many draft dodging politicians stand to profit from it. "Oh it's not just money, it's for religion." "Oh, it's not just for world domination and power, it's to annihilate entire ethnicities that caused us economic instability."
Answer me this, why waste valuable resources and money in a war unless you see a return?
There may be variables, but put them on a flow chart and I guarantee one way or another it all flows back to personal gain and profit.