Does the U.S. need such a large and expensive military? There are some limits we should have about the extent of our military power and how much our allies should depend on us, argues Christopher Preble, the Vice President for Defense and Foreign Policy Studies at the Cato Institute. U.S. military might is to be used sparingly and its costs are worth considering against its usefulness.

Christopher Preble: 
It’s true the U.S. military is a costly enterprise. It cost us more as a share of our total output during the Cold War, but in absolute dollar terms we’re spending about as much now as we spent during the Cold War, so the cost to maintain primacy has remained relatively high.

And the question is, could we spend much more on the military to cover some of the gaps between what we ask our military to do and the resources they have to carry out those missions? I think the answer is: we could spend more, but it’s not in our interest to do so, just spending more on the military won’t ensure that the military, for example, will be able to succeed, and some of the conflicts that it hasn’t yet achieved decisive victory.

I think it actually speaks to the limits of military power, that you can spend a lot and you can have the most exquisite military in the world, which we absolutely do, and yet that same military struggles to defeat determined adversaries wielding crude weapons in places like Iraq or Syria or Afghanistan. And I think that really does speak that just spending more money on the problem is not likely to solve the problem, it is likely to encourage us to get more deeply involved in some conflicts that might genuinely be intractable and that ultimately aren’t vital to U.S. national security.

I think that for a country as powerful as the United States, and especially a country with global interests and with a large and capable military, it’s really important to define ahead of time when that military will be used. I use some basic criteria that are consistent with things like the Weinberger Powell Doctrine from the Cold War and early post-Cold War period. Things like: what’s the national security interest at stake? What are we asking our military to do? Will the public support the mission even if the mission gets difficult and costly? Related, how are we going to pay for it? Will the war be paid for by, for example, a war tax or will we pay for it through debt like we did in World War II?

Those sorts of questions are important to ask before we send our military into harms way.

And I think that’s, again, the nature of the U.S. military, because it exists and it is so large and strong and in many places simultaneously, it’s fairly easy for that military to become involved in conflicts before we ask any of those questions. And so I think it’s really important for the American people and for American policymakers to keep in mind some basic criteria for when we use force. The last point I’d make is that war is a perilous enterprise. It involves the threat of violence and the destruction of property and therefore we shouldn't enter into it lightly.

And so I think when I think of restraint and an instinct of non-intervention, it's more about just a sort of skeptical eye, it's a sort of hesitance to use force. That doesn't mean never using force, it means thinking through it very, very carefully before we do.

I think that one of the great disservices we do to the military is to expect the American people to support it at all costs for any reason, and not expecting the American people to actually scrutinize the missions that we ask of the military to do.

In other words the greatest service that we can do to our veterans is to make sure that there are relatively few of them. That those who do go to war in defense of vital U.S. national security interests are doing so for the right set of reasons and I think it would almost be unpatriotic it seems to me for Americans to not think carefully about the wars that we ask our military to fight.

Most of us, the vast majority of us will have never served in the military, and the few of us who have I think I understand just what an important undertaking it is. And this country is quite accustomed to going to war without much debate and I think that really is a disservice to the military and to those who serve.

So a key component of primacy is to reassure our allies, and we do that for the most part to discourage them from taking measures to defend themselves. This might sound a little strange, but it actually made some sense after World War II when these countries were badly broken by World War II and endangered by the Soviet Union and Europe. These countries were in no position to defend themselves; they had to focus on rebuilding themselves, rebuilding themselves physically and also rebuilding themselves politically.

So the motion of reassurance as a means to discourage countries from doing more to defend themselves made certain sense at that time. The challenge however is that these countries have become quite stable and secure, and yet we never really revisited the bargain. And so we continue to have freeriding behavior or cheap riding behavior, countries not paying what they might need to pay in order to defend themselves.

The other problem with having too much reassurance is it can lead to moral hazard, it can lead to reckless driving. That is if allies believe that the United States has their back no matter what they might be inclined to behave in reckless ways, they might be inclined to take actions that they wouldn't if they were carrying the full burden and the risks. They might simply be discouraged from undertaking reasonable compromises on behalf of maintaining peace with their neighbors or in their region. And so the danger is that primacy encourages a kind of reckless behavior that ultimately is not conducive to long-term peace.

When the United States became the first nuclear weapons state there was some fear that many other countries would follow. The Soviet Union did, a few other countries did, Britain and France, but by the late 1950s early 1960s there was a pretty concerted effort to discourage other countries from going that route. The fear was that if many countries had nuclear weapons then the chances of their use would dramatically increase.

And a key part of reassurance is to discourage, particularly U.S. allies like Germany and Japan, from ever being tempted to develop nuclear weapons.

In fact I think in many respects that is one of the key arguments that defenders of primacy make, is that were it not for primacy there would be much, much more nuclear proliferation then there has been.

I think it’s also true however that primacy has encouraged some countries that are left out of the system, the so-called rogue states who want to develop nuclear weapons of their own to deter the United States from attacking them. We’ve seen that in places like North Korea, which is one of the poorest countries on the planet, but it nonetheless managed to develop a nuclear weapon, or the fear that places like Iran might want a nuclear weapon for precisely that same reason.

And so I think it’s fair to say that while U.S. primacy probably has discouraged some of our friends from developing nuclear weapons, it has sort of a mixed track record of discouraging our adversaries or potential adversaries from wanting nuclear weapons.

With the United States so heavily dependent upon military power as its main instrument of engagement with the rest of the world, it’s somewhat inevitable that the State Department and traditional diplomacy is sort of relegated to the back seat or to no seat at all.

And I think we’ve certainly seen that happen over the course of the last 15 or 20 years where the military receives the lion’s share of resources that go to engagement, and when the United States is asked or expected to interact with others it usually comes from people who are at least, if not carrying a weapon themselves, at least backed by people who are.

Of course that’s not the way the United States has always interacted with the rest of the world, traditional diplomacy has come both from the State Department and our actual official diplomats, but it’s also been carried by business people and NGOs and private actors who interact with the rest of the world.

And so I think one of the great dangers of primacy is that because it is defined as so much in military terms it means inevitably that diplomacy is sort of given short trip.