Actually, wars of aggression are almost never profitable. Accumulating riches via conquest is almost always a myth, because armies a) destroy much that is of value and b) are unbelievably expensive.
"Wealth through superior firepower" has hardly ever been achieved. Even Rome mostly got rich through trade after its armies conquered Europe and North Africa, and a lawful peace was imposed. Had everyone been economically rational pretty much the same end could have been achieved through trade (spoiler: not everyone is economically rational.)
Simple looting of the kind the Spanish engaged in in the New World was never a very good path to wealth, partly because its first effect was to create massive inflation (if you use gold as money and inject vase amounts of gold into your economy without increased productive capacity, you get inflation, not wealth.)
So the conditions of gaining wealth by war are very, very narrowly defined. It's not impossible, but it's amazingly difficult.
There are defensible moral reasons for engaging in mass organized violence--I support the current American efforts to kill people in Northern Iraq, for example--but economic rationality (profitability) is never one of them, because the first step to creating wealth is never to engage in the wholesale destruction of everything the creation of wealth depends on.