Re: A winning strategy?
Fighting ISIS is a case of spending enough money to move all the casualties to their side of the equation because they won't give up, don't care about anything other than winning and will happily use anything they can to cause mayhem.
We could spend far less fighting them but that would just get more of our people killed.
The simple maths of relative monetary values come into play if there's some level of comparability between the opposing sides. Many pre industrial wars were restrained by the ability to pay for them, Spain went bankrupt in their war with Elizabethan England and never recovered their former dominant position in western Europe. Several centuries of Anglo/French wars generally ended with a negotiated deal that didn't significantly damage either.