Strategy and Lord of the Rings

It’s a rainy afternoon, and so I’m watching The Two Towers, the second film in the Lord of the Rings series (Ed: I hated the books and didn’t even finish, but those movies are great).  Tolkien’s politics are not my own, not so much because of their noxiousness as simply their anachronism.  Regardless, the novels are rich in pretty interesting political implications, such as a close look at the difficulty of coalition-building among even well-intentioned partners.  However, what really got me thinking was the battle of Helm’s Deep, a supposedly impregnable fortress which is brought down by the placing of a bomb in a culvert, the sole weak point in the wall.  The point is that the fortress was really quite well-built for the mission of “resisting swarms of armed orcs” but less well-built for the mission of “resisting explosions”.
This is what I’m thinking about in the repeated trope that the U.S. needs to rebuild its military towards being able to win “small wars” like the conflicts in Iraq and Afghanistan.    This does make a certain amount of sense; a defeat-the-Soviets-in-the-Fulda-Gap military will be ill-suited towards a secure-the-Hindu-Kush mission.  What worries me about an expensive makeover of the U.S. military is that it is premised on one of two assumptions: either Iraq and Afghanistan will last arbitrarily long, or that we will be invading and occupying enough other small Third World nations that we need to be prepared.  Both of these are pretty troublesome assumptions.
In 1870, the French had an excellent army.  Honed by years of fighting in Algeria, it was a highly professional and experienced counterinsurgency force much like what the U.S. army is envisioning.  And when the shooting started on the Prussian frontier, they were absolutely destroyed.  The point being that missions you’re not prepared for are the devastating ones.  It should require a fairly high expectation of future utility in order to totally rebuild the military for such a specialized role…right?