Amid uncertainty over the outcome of the six-party negotiations on North Korea's nuclear weapons development, public concern is likely to focus on whether Pyongyang will live up to commitments it made to dismantle its nuclear weapons programme (already questionable) and whether it will pursue long-range nuclear missiles that could destroy an American city or, more immediately, Seoul and Tokyo. But the latter concern is not the most effective nuclear threat North Korea or other potential adversaries could pose.
A nuclear threat to American cities, if implemented, would certainly provoke massive US retaliation. There are better options for opponents: credible, cheaper and more suited to the US capabilities that adversaries would face. Since the cold war, the top US military priority, as stated in congressional testimonies, has been to deploy the world's most effective power projection forces. These forces have been used in the Balkans, the Persian Gulf and central Asia. A power projection force operates in or near hostile territory. It must rely on superior training, tactics and equipment. Joint force training, mobile communication and control, soldiers capable of individual initiative and precision-guided munitions have been key to US success.
Any power projection force needs air bases and ports of debarkation and logistics centres for sustained operations. These facilities must be rented or conquered. Their number is limited - a handful in Iraq, and not many more in east Asia, seven or so in Japan, some bases in South Korea, and a few others. These facilities are highly vulnerable even to inaccurate nuclear missile attacks. They are "soft targets", not "hardened" against nuclear weapons.
North Korea, with a couple of dozen warheads mounted on its intermediate-range No Dong missiles, or its longer-range Taepo Dong missiles, could threaten all the US assets mentioned above and have weapons left to threaten Tokyo and Seoul.
The US could destroy those North Korean military and nuclear assets it could locate. North Korean forces could retreat into the mountains and position for a protracted ground war. But would the US then launch a massive attack against North Korea with the threat still hanging over Japanese and South Korean cities?
The Pentagon's Quadrennial Defense Review envisages a force structure better suited to counter-terrorism and control of the seas and the sky, rather than focused on fighting two land wars simultaneously. The nuclear threat to essential US force-projection assets largely counterbalances the advantage provided by US conventional forces, without necessarily consigning whole cities and industrial bases to destruction. That latter threat can still be held in reserve by our adversaries.
Should this threat mature, it would undercut the credibility of US security guarantees in east Asia that have been the hallmark of US strategy in the region for more than half a century. Japan, South Korea and Taiwan all depend heavily on these guarantees for their security. This credibility has dissuaded each government from acquiring its own nuclear force. Such restraint, in turn, has permitted China to proceed at a more measured pace in its own nuclear weapons development programmes.
If key political and defence officials in Tokyo, Seoul and Taipei no longer believed in US guarantees because of the vulnerability of US military assets in the region to a North Korean nuclear missile attack, the consequences for their own security and for US national strategy could be profound. Although circumstances are quite different in the Middle East-Persian Gulf region, similar consequences could materialise if Iran or another hostile country developed a comparable nuclear missile capability.
A great deal is at stake in constraining the missile and nuclear weapons capabilities of North Korea and other rogue states. The US thus must utilise all the resources at its disposal, working constructively with its allies and other interested parties, to deny these states the capabilities they almost surely seek to acquire. A more resilient forward defence and deterrent posture is essential to an effective American global strategy.