Editor's note: Patrick M. Cronin is senior adviser and senior director of the Asia-Pacific Security Program at the nonpartisan Center for a New American Security in Washington.
Washington (CNN) -- North Korea's latest unprovoked military attack on South Korea -- the shelling of Yeonpyeong Island near the Northern Limit Line demarcating the Korean Peninsula's maritime boundary -- is a stark reminder that the Korean War never ended.
The first responsibility of the United States must remain the preservation of deterrence from outright return to war. The attacks leave the alliance with few good options for reprisal without risking a far less desirable renewal of conflict.
The United States must work with South Korea to bolster deterrence, check North Korean aggression and be ready to turn it back, but only if absolutely necessary. We will also have to operate without fully understanding the power at play in North Korea.
This year has already been a deadly one as an ailing Kim Jong Il accelerated the likely dynastic transition in power to an ill-prepared son who will be captive to aging generals in the Korean People's Army. In April, 46 South Korean crew members aboard the naval vessel Cheonan died when the vessel was ripped in two by a North Korean torpedo.
The shelling of Yeonpyeong has now left new casualties, and motives for the attack remain numerous and unclear. Could this be Kim Jong-un's next lesson regarding the use of force? That is, are the North's generals demonstrating how they can literally get away with murder with limited uses of force despite the superior military forces of the South Korea-U.S. alliance?
Perhaps, but is the force intended to advance a larger, coherent political objective? Clearly consolidating power during an uncertain transition is a serious goal. But so, too, is Pyongyang's effort to convince the United States that it should deal directly with North Korea.
Furthermore, based on the sudden willingness to show off its nuclear enrichment facility to American visitors, North Korea appears to be saying it is time for the United States to sit down for direct negotiations as two fellow members of the nuclear club, rather than continue the diplomatic talks among six nations concerned with the nuclear issue.
We can clearly see that the North Korean regime is delusional about what it can achieve. But what we do not and cannot know given the North's opacity is North Korean intentions -- or even North Korea's future, although it is certainly not likely to be a bright one under the current regime.
We can take some solace in the fact that a visit to each side of the demilitarized zone clearly reveals that looking south appears far more menacing than peering into north. Even so, deterrence is dynamic and cannot be assumed to endure and certainly not without concerted action to bolster it.
Earlier this year officials in Seoul and Washington wisely agreed to delay the wartime return of operational control back to South Korea. Given this year of living dangerously, that seems a prudent decision, because it will give the allies even more time to make demonstratively clear the strength and capabilities of South Korean forces lest an increasingly emboldened North Korea tries to push its luck too far.
During this interim period, it is an ideal time both to strengthen South Korean military capabilities further but also contingency plans and readiness. Not only should this involve the U.S.-South Korean alliance but Japan as well, given its proximity and the vital bases there.
Meanwhile, we should not give up on providing opportunities for China to demonstrate that it is serious about helping enforce a rules-based order, including the denuclearization of the Korean Peninsula.
Still, it will be hard to build trust after China's cavalier refusal to rein in North Korea following the sinking of Cheonan. China is playing for keeps -- aiming to exert greater influence over its region -- even if that means tolerating the destabilizing belligerence of its neighbor.
A North Korea that thinks it can get away with anything is a dangerous North Korea. The military exercises called for after Cheonan are not enough, especially given this latest attack. Further defensive actions to fortify the border area would seem to be in order.
At the end of the day, like Yeonpyeong Island itself, we are left in a remote realm of security. Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, recently said that North Korea remains predictable in its unpredictability. Quite so; only more now than ever before.
The opinions expressed in this commentary are solely those of Patrick M. Cronin.