As usual, most commentary on North Korea's rocket launch last week focuses on the politics and diplomacy of Pyongyang's delinquency. But it is worth exploring the strategic implications more specifically. These are significant, but not straightforward.

The apparently successful launch of a three-stage rocket makes it rather clearer than before that North Korea has both the capacity and the intention to build an intercontinental-range ballistic missile (ICBM). It is now prudent to expect that in perhaps as little as a decade, if North Korea survives in its present form, it may well have an operational ICBM capability. This would give Pyongyang the capacity to deliver a small number of probably relatively low-yield nuclear warheads onto American cities. 

The key question, therefore, is what this would mean for strategic affairs in Northeast Asia over coming decades.

The first thing to say is what it doesn't mean. It does not mean North Korea has any rational options to initiate an unprovoked nuclear attack on the US, because that would certainly produce a totally devastating US response. Nor does it make much if any difference to Pyongyang's capacity to deter a nuclear, or regime-threatening conventional, attack on North Korea. Its existing medium-range nuclear delivery options bring plenty of high-value targets within range of its nuclear forces today, so Pyongyang already has the capacity to deter military action which potential attackers would fear might cross Pyongyang's red lines.

But an ICBM capability would undermine the deterrent umbrella extended by the US to its Asian allies.

Extended deterrence depends on the credibility (to both the adversary and the ally) of US threats to respond to any nuclear attack on the ally with a US nuclear attack on the adversary. Such credibility depends a great deal on whether the adversary has the capacity to hit back at the US. As long as North Korea has no credible capacity to target America itself, a US retaliatory strike on the North carries relatively low risks for the US itself. 

But if the North can hit back, the costs for the US go up dramatically, and the credibility of the US threat goes down. In a crisis, everyone will be asking whether stopping North Korea doing whatever it wants to do is important enough to America to risk a nuclear attack on Honolulu or LA.

Of course, America can fix this if it can destroy North Korea's ICBMs early in the crisis. This would be easy as long as the missiles are as exposed and vulnerable, but of course if Pyongyang is serious about an ICBM force it will do whatever it can to make them more survivable, and would probably succeed to some extent at least. Moreover, conventional strikes against North's ICBMs would not be risk-free for the US even if they were likely to succeed, because Pyongyang could credibly threaten nuclear retaliation with its medium-range forces. So we should not assume that the North's ICBMs can be simply blown away. 

How serious is this? That depends on how seriously we see the risk of North Korea adopting an aggressive rather than defensive strategic posture over the next few decades. The more likely it is that Pyongyang might try to invade the South or attack Japan, the more worrying it is that US extended deterrence might be weakened by North Korean ICBMs. And if the argument presented here is correct, then ICBMs only make sense for the North if it does harbour aggressive intentions, because they do not substantially increase the North's capacity to deter on attack on itself. 

On the other hand, North Korea is a weak state surrounded by strong neighbours. Unlike Iran, for example, it has no serious chance of being able to extend its territory or political clout at its neighbours' expense – with or without ICBMs. This makes the ICBM program look like a bad investment for Pyongyang.

And what of North Korea's neighbours? Clearly, weakened US extended deterrence means higher incentives for Japan and South Korea to build nuclear forces of their own. But I doubt Pyongyang's moves add much to the already growing incentives for Japan at least to build a deterrent capability of its own. It worries about China, and China already has ICBMs, so US extended deterrence against China is already weaker than most people assume.

Photo by Flickr user oracle monkey.