Most wars are fought on the basis of how the weapons a particular Army has, and the kind of training that Armies officers and NCOs have gotten, can be used(1). Preparing for a particular war, in a particular way, using a particular kind of force, with particular kinds of weapons, can leed to failure once a war surfaces because rarely does it turn out to be the war you expected. It's an age old problem. Rumsfeld fell headlong into that problem. It was far from being his fault alone though. The United States military has been shackled to, and by, conventional warfare thinking, and weapons procurements, ever since WWII. Consequently that's the filter through which they see the worlds trouble spots.
(1)No better example of this can be found then Pakistan's Army. Everything Pakistan's Army, and intelligence service, does is based on a projected war with India. The way they have handled the Taliban is based on a confrontation with India. The diplomatic langue they use during public conversations with us is for Pakistani consumption and based on protecting the use of their forces for the expected confrontation with India. That's all Pakistan's military and secret intelligence service is for, and nothing else. They could give a flying bleep about us, except for our money. That's what Richard Holbrooke was up against. Well, that's who he had in one corner. In the other corner is a crooked nut-job who spends most of his time off his meds.
bsb, Have Gun Will Travel
p.s. In case someone couldn't figure it out, the civil war reference was a joke.