Last week, the Trump administration circulated a new U.N. resolution that would authorize inspections of vessels delivering certain goods to North Korea. While the inspections would not amount to a total naval blockade, and would instead focus on intercepting vessels carrying fuel, textiles and military technologies, they would represent a significant new step in the ongoing crisis.
The question is, would this action move the diplomatic needle towards an agreement that ends the crisis?
Perhaps, perhaps not.
One benefit of inspecting North Korean-destined vessels would be in showing Kim Jong Un that the U.S. is willing to use force to address the threat he poses. That realization would force Kim to take Trump's threats more seriously and might deter him from further ballistic missile tests. Also relevant here is that North Korea's ability to contest inspections is highly limited. Its navy, though improving in submarine capabilities, cannot operate hundreds of miles offshore (where most interdictions would occur).
Second, a targeted-blockade would bring a multilateral component to the North Korea crisis, forcing China and Russia to stand against an alliance of nations rather than just the U.S., South Korea, and Japan. It is likely that Australia, Britain, France, New Zealand, and India would contribute forces to this effort. Witnessing that effort, Beijing would see that its failure to exert significant pressure on Pyongyang is risking China's broader diplomatic and trade interests. (Speaking of India, its government is increasingly frustrated with China and has voiced a willingness to work with us on North Korea. The U.S. should draw its pro-American government into a closer alliance.)
Finally, while North Korea could obviously divert trade through Chinese ports and then across its land border, or simply across its land border, the costs of doing so would be significant for the already impoverished nation. At the margin, every little bit of extra pressure hurts Kim Jong Un's regime.
Then again, a naval blockade would pose complications.
For one, absent a U.N. resolution authorizing any inspections, the U.S. would struggle to get allies like Britain to support the blockade. As I've explained, America's allies are increasingly hesitant about risking their own prestige and personnel in helping the U.S. to resolve this situation.
Second, the U.S. Navy would need to divert a significant array of ships, planes, and other supporting capabilities to enforce the blockade. For an already overstretched navy, this would be an expensive gambit. Don't get me wrong, it absolutely could be done, it would just be difficult. It would, for example, require a reduction of navy port visits to allied nations.
Third, what if the Chinese and Russians decided to oppose a blockade? Consider what might happen if the U.S. Navy boarded a Chinese or Russian flagged vessel, or a North Korean vessel that had been reflagged as Chinese or Russian. The risks of a major international showdown would grow quickly and significantly.
Ultimately, this complicated mix of positives and negatives speaks the deeper challenge in pressuring North Korea: there are few good options.
My own opinion is that we should hold off a naval blockade for now. As I've noted, two better alternatives would be the introduction of sanctions on global financial entities that assist North Korea, and the shooting down of North Korean intercontinental ballistic missiles. While those actions would upset China and Russia, they would also keep the crisis in the purview of the diplomats. The U.S. objective should be to motivate Chinese action that strangles North Korea's access to foreign capital. That outcome is the best way to force Kim into serious negotiations on his ballistic missile program.
We'll just have to wait and see what Trump decides to do. Nevertheless, it is worth noting that Secretary of Defense Jim Mattis is a proponent of naval blockades. In 2015, after leaving military service but prior to entering the Trump administration, Mattis suggested naval blockades would effectively enforce Iran's compliance with its P5+1 nuclear agreement.