One of the most enduring concepts in international relations theory—particularly the Realist variant of it— is the offense-defense balance. The offense-defense balance is basically, in two scholars’ estimation, “the ratio of the cost of the forces the attacker requires to take territory to the cost of the forces the defender has deployed.”
Proponents of the offense-defense balance argue that when military technology and doctrine favor the offense, the security dilemma is more acute and war is more likely. For example, proponents of this theory hold that one reason that WWI broke out was because all the parties believed that the opening salvos of the war would be decisive in determining its outcome, and therefore felt they had to act first since so much advantage was gained from doing so.
Of course, the military technology and doctrine at the time of WWI did not in any way favor the offense; quite the contrary. Thus, one of the most stinging critiques of offensive-defensive balance theory is that it is impossible to distinguish between weapons and doctrine that are purely offensive versus those that are purely defensive in nature. As Michael Brown has summarized these critics’ argument, "Whether a weapon is offensive or defensive depends on the situation in which it is used."
Given the importance of preventing a conflict between the U.S. and China, it’s worth analyzing the military balance in the Western Pacific through the lenses of the offense-defense balance. Since, the “offensiveness and defensiveness of many weapons is ambiguous,” one can gain more from considering their military doctrines (or concepts)—AirSea Battle (ASB) and Anti-Access/Area-Denial (A2/AD)— which give us a better sense of how these capabilities would be deployed.
While the U.S. military struggles to precisely define ASB, even a less than complete understanding of it leaves little doubt that—at least with current capabilities— ASB calls for offensive-oriented action. This is explained well by the Rand Corporation’s Terrence Kelly and David Gompert in an excellent recent commentary piece on Foreign Policy.
As the authors point out, ASB seeks to prevent the PLA from denying U.S. and allied forces access to the first island chain by eliminating the A2/AD systems of systems China has built to achieve that. Kelly and Gompert write, “According to Air-Sea Battle, U.S. forces would launch physical attacks and cyberattacks against the enemy's ‘kill-chain’ of sensors and weaponry in order to disrupt its command-and-control systems, wreck its launch platforms (including aircraft, ships, and missile sites), and finally defeat the weapons they actually fire.”
Given the presumed vulnerability of U.S. military assets to PLA A2/AD capabilities like DF-21D anti-ship ballistic missiles (ASBMs) and submarines, the U.S. would have to do this before China had attacked. The inevitable reality then, is “that Air-Sea Battle suggests the United States would strike China before China strikes U.S. forces.”
Kelly and Gompert further point out, in the best tradition of offensive-defensive balance theory, that this creates an inherently unstable situation. After all, the PLA understands the imperative for the U.S. to strike first under ASB, and as a result it is tempted to preempt the U.S. out of fear Washington will neutralize its A2/AD assets.
To prevent this sort of destabilizing conflict spiral, the authors propose a number of steps the U.S. can take. Along with increasing the range of U.S. strike forces and dispersing U.S. military capabilities in the region—which the Pentagon already appears intent on doing— the authors suggest that the U.S. and allies should buildup their own A2/AD capabilities in the region. Were U.S. allies in the region to have their own A2/AD forces, the authors argue, there would be less incentive to strike first as they could simply repel a PLA attack.
This presupposes that A2/AD is an inherently defensive capability. In many ways, it seems obvious that it is. After all, A2/AD essentially attempts to prevent other militaries from operating close to one’s shores or the shores of a county where one has a significant military presence. In China’s case, building up A2/AD capabilities reduces its vulnerability to being attacked by U.S. air and naval forces operating in close proximity to China.
It’s quite likely that China itself sees its fielding of A2/AD capabilities in this manner. It is equally clear, however, that the U.S. does not see it as so. Rather, Washington fears that China is trying to deny the U.S. military the ability to operate within the first island chain so Beijing can launch offensive military attacks against its weaker neighbors such as Taiwan and the Philippines.
This goes to the heart of the critique of the offensive-defensive balance; namely, that you can’t divorce military capabilities from their political applications. Missile defense would at first seem purely defensive (hence the name). But if one country, after fielding an effective missile defense system, uses this added cover to launch attacks on another country, then the missile defense is being used for offensive ends.
The same goes with A2/AD. Determining whether A2/AD is a defensive doctrine requires knowing what the objectives of the country fielding it are. For instance, if the U.S. and its allies erected A2/AD capabilities in an arc around China, they could theoretically use this to institute a blockade against the Chinese mainland. As an American, I’m confident the U.S. wouldn’t do this unless it had a strong justification. At the same time, I’m equally confident that China might see things differently, and we’d probably disagree over what constitutes adequate justification.
Still, it could be argued that if both the U.S. and China had effective A2/AD capabilities deployed in the region, the balance would still favor the defense and therefore would reduce the likelihood of war. But this logic only works if neither power had any effective offensive strike capabilities. After all, China’s A2/AD capabilities have not made Beijing any less fearful that the U.S. will neutralize these assets through preemptive or preventive strikes. And since many of the same weapon systems that are used for A2/AD—such as missiles, submarines and cyberwarfare— could also be used to neutralize other A2/AD systems in close proximity, the U.S. fielding A2/AD capabilities in the region wouldn’t seemingly reduce the security dilemma that exists in the Western Pacific. In fact, it could worsen it by increasing China’s perceived vulnerability.