Relationships Between Highly Asymmetric Nuclear Powers

By Rod Lyon

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The current tensions between Washington and Pyongyang aren’t just about history. Nor are they simply the result of personal frictions between Donald Trump and Kim Jong-un. At their core, they reflect the difficulties that typically attend adversarial relationships between two highly asymmetric nuclear powers. Bernard Brodie, one of the doyens of deterrence thinking during the early days of the Cold War, canvassed some of the problems in this sort of relationship in his 1958 essay, The anatomy of deterrence. There he considered how the Soviet Union might be strategically hampered by the emergence of a much inferior adversary which could, however, threaten nuclear damage to a small number of Soviet cities. The following extract is taken from pages 7–9 of his essay: [D]eterrence effect in itself does not depend on superiority … Let us assume that a menaced small nation could threaten the Soviet Union with only a single thermonuclear bomb, which, however, it could certainly deliver on Moscow if attacked … [This] would be sufficient to give the Soviet government much pause … If we think of five to ten H-bombs delivered on as many … cities, the deterrence would no doubt be significantly greater.

If we attempt to plot a curve denoting “deterrence effect” as a function of the numbers of thermonuclear devices expected to fall on the aggressor’s cities … we can surmise that the curve begins at a rather high level of deterrence for the first such bomb, and that while it moves significantly higher as the number of bombs moves beyond one, it does so at a decreasing rate. At a relatively modest number (probably well short of a hundred) the curve is closely approaching the horizontal.

Let’s bring that logic into the current setting. If Brodie’s right, a North Korea equipped with ‘a relatively modest number’ of thermonuclear-tipped ICBMs can be almost as effective in deterring the much more amply-equipped U.S. as the U.S. is in deterring the much smaller North Korea.

Brodie’s assessment is a painful lesson in the truism that nuclear weapons are great equalisers. Sometimes that’s a good thing, because smaller nuclear powers can be forces for good. Cases in which a smaller status quo power uses nuclear weapons to offset a larger revisionist power—France against the Soviet Union during the Cold War, for example—suggest that some asymmetric relationships can make a positive contribution to international stability.

Still, there the asymmetry wasn’t great. Both France and the Soviet Union were members of the Permanent Five of the UN Security Council, responsible for managing international crises on a regular basis.

But weapons that make much smaller powers with revisionist agendas ‘equal’ to great powers with status quo agendas look inherently problematic. A high percentage of recent analysis on the emerging deterrence relationship between Washington and Pyongyang has fixated upon the question of whether Kim Jong-un is rational and ‘deterrable’—that is, on whether the U.S. can reliably deter North Korea.

But turn that question around. How much deterrence of the U.S. does Kim believe he has now bought for himself? And what new freedom of manoeuvre does he think he now enjoys in Northeast Asia because of his capabilities?

One of the main threats that a smaller nuclear power poses for a larger one concerns those long-term effects that even a relatively limited nuclear exchange between the two might have on other, more important, nuclear balances. That threat was always at the core of French nuclear thinking—France couldn’t hope to defeat the Soviet Union in an all-out nuclear exchange, but it could threaten to ‘rip an arm off’ the Soviet Union and leave it a one-armed superpower against its nuclear peers.

That threat has to be a worry for Washington in the event that push ever comes to shove with a nuclear-armed North Korea. Of course the U.S. could defeat North Korea. But at what cost? A nuclear-damaged America would be relatively disadvantaged vis-à-vis Russia and China, less well placed to protect both itself and its allies.

Well, some might argue, Kim Jong-un doesn’t—yet—have any proven capabilities to target the continental U.S.. True, his ICBM tests were flown on highly lofted trajectories. Still, intelligence estimates suggest such a capability is not far away. That’s what lends both urgency and importance to finding a solution to the North Korean nuclear problem.

A relationship of mutual nuclear vulnerability between one country with almost no equity in the international order and another with deep equity in the same order wouldn’t be stabilising. Diplomacy might yet find a solution to that problem. But if it doesn’t, we shouldn’t assume that a comfortable, long-term nuclear deterrence relationship will miraculously unfold as a simple, benign alternative.