Seydlitz89 raised an interesting point in a comment to a my post, The Future of Conflict:

From a Clausewitzian perspective, specific political interests/objective politics runs what passes for US policy today, what Max Weber would have called political or adventure capitalism. Also the character of the state defines the character of its policies. Thus reducing the defense budget is definitely not in the cards. Rather the tendency will be to muddle through until the collapse, much as Spain did in the 17th Century. . .

You can scroll down through the comments on that post to read my witty riposte.

It can sometime seem that today’s trends represent a stable condition, but we all know that defense budgets can’t just keep going up. Here are the DoD budgets over the last 60 years. As you can see, they obey the general law that whatever goes up must come down.

But there’s more to it than that. US defense funding seems to reflect periodic fads, when we couldn’t add money to the budget fast enough. Korea and Vietnam have underlying bases, of course, and even the Reagan spend-up could point to the mighty Soviet Union to justify its increases (which if you look closely, actually started under Jimmy Carter!)

But then a strange thing happened. Each fad would evaporate as quickly as it came, and the rate of descent would roughly mirror the rate of the build-up. My prediction is that we’re going to see the same result this time. Incidentally, the budgets projected by the first Reagan administration assumed that DoD spending would continue to grow at about the same rate through the second administration. Here’s Chuck Spinney’s summary chart of that period [the black lines represent administration budget projections, each made in the year before that particular line begins].

What might cause a steep drop-off in our current defense spending?

1. Unlike in previous build-ups, there isn’t a threat to justify spending at this level: No conventional wars, we don’t have 500,000 troops in Southeast Asia, and Russia is not the Soviet Union (neither is China).
2. Soon, many other demands for money will come into play. I can’t predict exactly when or how much, but candidates include Medicare (wait until the impact of the 10.5% cut in Medicare reimbursement rates starts to take hold — note to service personnel, this affects TRICARE, too), the continuing financial crisis, demands for relief by homebuyers (and banks and brokers), a potential for a severe recession, possible movement out of the dollar by Russia, China, Japan, etc. Or pick your own black swan. Candidates will say what they think will get them elected, then reality will set in.
3. Once the zeitgeist shifts directions, change is swift and dramatic.
4. Did I mention that there’s no real threat, so it will be easy to think up narratives explaining why cutting DoD is in the national interest?

Notice that point 4 is rationalization, story-telling. S89 mentioned in another comment that I was assuming “rational behavior.” No, I’m not, unless you want to infer rationality into the collective behavior of our elected officials.