What would Clausewitz say about the war against the Islamic State in Iraq and the Levant (ISIL)? As the Prussian sage and his fellow greats of strategic theory might counsel, America is waging an “unlimited war by contingent” against ISIL. Last year President Barack Obama vowed to “degrade and ultimately destroy” the terror state, yet ruled out more than modest air and sea forces to execute this ambitious mission. U.S. ground warfare was out. That raises the question whether the regional contenders battling the Islamic State — the Iraqi army, the Peshmerga, various militias — together comprise a force capable of winning with aerial fire support. Fitful progress on the ground leaves that question open, the allies’ recent re-conquest of Ramadi notwithstanding.

The administration has backtracked from its “no boots on the ground” position since, ordering a “specialized expeditionary targeting force” to Iraq early this month. But with overall troop numbers fixed at 3,550, a token number, the sages might voice bafflement at this misbegotten approach to strategy. You cannot know in advance how many troops it will take to crush your enemies and see them driven before you.

Such a strategy is a contradiction in terms that is fated to disappoint. Why? Let us parse the first part of the phrase unlimited war by contingent. More than an arcane point of strategic theory is at stake here. Wars are generally limited by their strategic and political ends — not by the means, measured in personnel, ships, airplanes, and armaments that the leadership earmarks for waging war. Political leaders determine what they want out of the enterprise, ask themselves how much they want it, and allocate the resources necessary to achieve it. Politics drives strategy drives the amount of force used — that’s Clausewitz 101.

In strategic parlance, a belligerent prosecuting an unlimited war is after big goals. Eradicating a foe’s political existence is a quintessential unlimited end. Or combatants can go beyond regime change. They can make a desert and call it peace, destroying an enemy society altogether — much as Rome did after its final onslaught on Carthage. President Obama placed the counter-ISIL campaign in the unlimited category. In effect, Washington announced that it’s prepared to devote whatever it takes for as long as it takes.

Purpose, then, determines how warring states deploy power. That is what Clausewitz means when he proclaims that the value a combatant assigns the “political object” governs “the sacrifices to be made for it in magnitude and also in duration.” Trivial aims summon forth short-lived endeavors of meager amplitude. Big, passionately sought goals — such as the destruction of a political entity that holds and governs territory — warrant big outlays of lives, treasure, and military hardware, typically for a long time. This logic holds doubly in a fight to the finish, when an opponent bestriding death ground will presumably do his utmost to survive.

Or at least cost-benefit logic should hold. Rather than estimate what degrading and destroying ISIL would take and committing the necessary forces to the fray, Washington decided in advance what it was willing to send — namely fighter, attack, and bomber jets — and dispatched that contingent to the theater. Wittingly or not, administration officials limited this politically unlimited war by the size and configuration of the military contingent they were prepared to send in harm’s way. That’s something like proclaiming you’re going to buy a sleek, new 7-Series BMW for $10,000, getting a cashier’s check for that sum, and trundling off to the dealership to get the car. Good luck closing that deal. And good luck closing the deal in the Levant without deploying ground-pounders in substantial numbers. You pay the price for your political objectives, and the antagonist from whom you’re trying to wrest those objectives has every incentive to keep marking up the price.

Aerial bombardment may keep ISIL in check. It has thus far, and that is a worthwhile contribution. It will not put an end to ISIL unless the United States or its allies assemble a ground force capable of crushing the terror army, dismantling the military and political leadership, and preventing the would-be caliphate from rising again. If Washington does not will the means necessary to accomplish that, it does not will the ends.

Now, there is something to be said for prosecuting war by contingent under certain circumstances. It is a time-honored way to make trouble for a foe at low cost to yourself — if mischief-making is your purpose. It is just not a standalone or war-winning strategy. One example from classical antiquity: During the Peloponnesian War, the Athenians sent an expeditionary fleet and army to occupy Sicily, one of the breadbaskets of the Mediterranean world. Their archenemy Sparta got wind of the Sicilian campaign and dispatched the able soldier Gylippus to advise Syracuse, the island’s dominant city-state and the Athenian expedition’s chief target. Athens lost its force to a man owing in large measure to Gylippus’ advice. That constituted one heckuva return on investment for the Spartans.

Sea-power theorist Julian S. Corbett — think of the fin de siècle English scribe as Clausewitz riding the waves — explores the concept of war by contingent in some depth. Corbett points to Lord Wellington’s expeditionary force in Iberia during the Napoleonic Wars. Supported logistically by the Royal Navy, Wellington’s modest-sized army imposed a second front on Napoleon, dispersed French forces, and fought alongside partisans to make life hell for the French Army. The British expedition proved so nettlesome that the little emperor termed it France’s “Spanish Ulcer.”

Limited endeavors, then, can make an outsized difference in a larger struggle. How to choose places and methods to give a foe a nagging ulcer? Would-be troublemakers look for things away from the major fighting that their enemies must defend at lopsidedly unfavorable cost. Even so, ulcers are not fatal. Allocating a martial contingent — Wellington’s army then, U.S. Navy, Marine, and Air Force warbirds today — constitutes an excellent way to contain and degrade an adversary. But destroy Napoleonic hosts, or ISIL, through secondary ventures prosecuted on the cheap? Forget about it.

Next, a theoretical point about airpower. As one of Newport’s own theorists, J. C. Wylie, teaches, it is possible to destroy things from aloft without controlling events on the ground. And control — not destruction for its own sake — is the object of military strategy. For Wylie, mistaking destruction for control is a failing peculiar to airpower proponents. It misleads them into thinking airpower wins wars on its own. Instead, he insists, it is the soldier — the “man on the scene with a gun” — who’s the arbiter of wartime victory and defeat. All military efforts must be geared to getting soldiers into the right positions on the map in sufficient numbers and with capability to control affairs. In the campaign against ISIL, that means U.S. Army or Marine troops, allied troops, or some composite fighting force.

Lastly, though, there is a perverse dimension to the anti-ISIL air campaign: The more successful air strikes are, the less successful alliance-building and alliance-maintenance (the key to any ground component) is apt to be. Think about it. What happens if aerial bombardment contains ISIL geographically, as President Obama plausibly claims it has done? If aviators stymie the Islamic State’s efforts at expansion, they help current and potential Middle East allies step off death ground. In so doing they reduce the incentive for these countries to shoulder the burden of ground combat.

Such is the topsy-turvy challenge before Washington. Administration leaders must put policy and strategy, not artificial limits on military means, in charge of the counter-ISIL campaign. If U.S. policy is to destroy ISIL, let us figure out what that entails in terms of ground, air, and sea forces and set those forces in motion. If it is to contain ISIL through airpower, let us say that and resign ourselves to an open-ended effort promising few satisfactions.

The United States can wage unlimited war against the Islamic State, or it can wage war by contingent. Trying to do both opens up a world of strategic problems.

James Holmes is Professor of Strategy at the Naval War College. The views voiced here are his alone.

Photo credit: Mass Communication Specialist 3rd Class Robert Burck, U.S. Navy