A DF-31A Intercontinental Ballistic Missile [ICBM] of the PLA

It wouldn’t be a new cold war without an accelerating nuclear arms race. The Pentagon reported last week that China is undertaking a significant nuclear build-up, which will double the size of its arsenal by 2030. That development isn’t surprising, given China’s strategic situation. But it’s still distinctly challenging for the U.S., because it compounds the worsening military situation in the western Pacific.

Since its first nuclear test in 1964, Beijing has possessed a relatively modest deterrent — an arsenal numbering first in the dozens and now in the low 200s of warheads.

China is now rapidly expanding that deterrent, building more and better intercontinental ballistic missiles that will improve its ability to hit targets in the U.S. It is developing a more robust “triad” — a combination of long-range bombers, ballistic missile submarines and land-based missiles — that will make its nuclear capabilities more survivable against any potential attack. The Defence Department projects that in addition to the doubling of China’s nuclear warhead stockpiles over a decade, the number of warheads that can strike the U.S. will grow to roughly 200 by 2025. The People’s Liberation Army is also improving the readiness of its nuclear forces, by developing a launch-on-warning capability — a posture in which Beijing would respond to an incoming nuclear attack with a retaliatory strike before enemy warheads hit their targets.

In one sense, it’s not shocking that a country involved in a deepening rivalry with U.S. — which has about 1,400 deployed nuclear warheads — would improve its nuclear capabilities as its power grows. The more challenging question is how much, and in what ways, the Chinese build-up matters.

One interpretation is that it doesn’t. Even with 400-plus warheads, China will be far short of nuclear parity with the U.S. Beijing has retained its longstanding, if ambiguous, “no first use” policy, and it seems highly unlikely that China would use nuclear weapons in an unprovoked attack. Indeed, the scholars Fiona Cunningham and M. Taylor Fravel have argued that China remains very hesitant to employ nuclear weapons in most conflicts, for fear that any nuclear war could spin out of control. From this perspective, the Chinese build-up might be a strategic nothing-burger. Yet this interpretation raises the obvious question of why the Chinese would engage in a pointless build-up.

A second interpretation holds that the build-up is strategically meaningful, but in a good way. Nuclear strategists have long warned that it can be dangerous for both sides when one actor fears that its nuclear forces are vulnerable to a disarming first strike. In a crisis, an insecure nuclear power might feel pressure to use or lose its arsenal — to fire off its warheads before they are wiped out by an enemy strike. For this reason, Secretary of Defence Robert McNamara actually worried about the vulnerability of Soviet ICBMs during the 1960s. This hypothesis is somewhat plausible, given concerns that U.S. conventional strikes on Chinese command-and-control assets could accidentally make Beijing fear losing contact with its nuclear forces. The trouble is that nuclear stability can, paradoxically, be destabilizing.

This possibility underpins a third interpretation — that the Chinese build-up will make life harder for the U.S. America’s nuclear shield has typically been designed to shore up the conventional defence of exposed allies. During the Cold War, NATO would have struggled to stop a Soviet invasion with conventional forces, so it had to be willing to escalate to nuclear war. For that threat to be believable, the U.S. had to have a meaningful “damage-limitation” capability — the ability to wipe out most or all Soviet nuclear forces, so Moscow could not inflict catastrophic harm on America in a retaliatory attack.

There are similar considerations at work today. As the conventional military balance in the Taiwan Strait deteriorates, the U.S. might feel compelled to threaten nuclear escalation to deter or defeat a Chinese attack. But that option is only credible if the U.S. can destroy enough of China’s nuclear arsenal — on the ground or with missile defences — to prevent a devastating riposte. As one Chinese military official remarked during a crisis over Taiwan in 1996, America would surely not save Taipei if it meant losing Los Angeles.

This is where China’s build-up matters. As recently as the mid-2000s, Beijing’s arsenal was small and vulnerable enough that some experts believed that the U.S. could perhaps destroy it in a first strike. Several years later, the scholar Thomas Christensen wrote that the Chinese themselves worried that they had only a tenuous second-strike capability, and were improving their arsenal accordingly. If China’s nuclear expansion removes any remaining possibility of an effective U.S. first strike, then Washington might well be deterred from going nuclear in the first place. And that, in turn, could make Beijing more confident in its ability to wage a winning conventional war as the balance of power shifts in its favour.

There’s no easy fix, from an American perspective. The U.S. could try to improve its ability to target China’s expanding nuclear forces, but that would be very hard and expensive when resources for nuclear modernization are already stretched quite thin. It could look for limited nuclear options against China: strikes that use a small number of weapons simply to demonstrate that the war will get out of hand if Beijing doesn’t call it quits. Yet there is no guarantee that limited strikes wouldn’t spiral into something more catastrophic. Or Washington could simply defend its allies and partners conventionally. That’s the most attractive option in theory, but one that will also require lots of money and innovation as China’s military capabilities improve.

China’s nuclear build-up thus demonstrates two uncomfortable truths. First, that the requirements of strategic stability and American strategy are often at odds. In theory, the most stable situation is one of perfect mutual assured destruction, in which neither side has an incentive to use nuclear weapons first because neither side can escape a society-shattering response. But America’s global commitments require the advantage provided by strategic instability if the U.S. is to reinforce those commitments with the threat of nuclear escalation. This was why the U.S. never really accepted mutual assured destruction during the Cold War, and why the emergence of a still-inferior but more secure Chinese arsenal is troubling.

Second, the dilemmas of defence in the western Pacific are only getting harder. The overriding thrust of Chinese military modernization for a quarter-century has been neutralizing the conventional advantages — long-range power projection, space-enabled precision-strike capabilities — that would allow Washington to intervene decisively in a war in China’s neighbourhood. The People’s Liberation Army is narrowing the nuclear imbalance that backstops an eroding conventional edge. A revisionist state is getting closer to the point at which it might be able to expand its influence by force. That has, historically, been a formula for trouble.