Even when the US is at the zenith of its power, things don't seem so easy and smooth. For example, a small and impoverished country like North Korea is proving a hard nut to crack. Its brinkmanship on the nuclear question is a serious constraint on US power, for fear that things could get out of control with dire consequences all around.
Even if one were to discount North Korea's nuclear deterrent (it is believed to have a couple of atomic bombs, with more in the process), the sheer scale of its conventional military power, in terms of threatening South Korea and Japan, is scary. With its million-strong army and an array of weapon systems from artillery to missiles, Seoul is within easy reach. And Japan is a missile target.
South Korea is understandably nervous, with much of the blame for igniting the crisis directed at Washington. As Elizabeth Economy and Eugene Matthews point out, "Anti-US sentiment in South Korea is at its highest level since the country's founding in 1948. Most South Koreans believe that the United States does not appreciate the danger it [South Korea] confronts on a daily basis from North Korea, and they see America's recent harsh rhetoric as having exacerbated that danger, by increasing the North's sense of isolation and paranoia."
There is also a pervasive sense of danger in Japan. The Japanese probably regard it as the most dangerous scenario since World War II. There is a growing political constituency favoring militarization, including nuclear weapons. Taken to its logical conclusion, its ripple effects in the region are too horrible to imagine.
In other words, the crisis on the Korean Peninsula requires urgent resolution. But it is increasingly realized that a pre-emptive strike is not a feasible proposition because of its unpredictable consequences. The scale of human and material destruction is too grim to contemplate. This leaves diplomacy as the preferred alternative.
Diplomacy has two facets: coercive and persuasive. Both require international cooperation. Regarding the first, UN-approved international sanctions are the obvious course. Pyongyang, though, has raised the stakes by declaring that it would regard sanctions as a declaration of war. In any case, with China effectively ruling out a Security Council-approved sanctions regime (with its veto), it might not come to that. Any attempt to cobble together a sanctions regime outside the UN will have to reckon both with Pyongyang and Beijing.
Regarding persuasion, China is again the crucial factor. And it won't work unless Pyongyang is clear about the alternative. Beijing, therefore, would need to forewarn Pyongyang that unless it abandoned the nuclear path, it would be on its own. Considering Pyongyang's overwhelming dependence on Beijing for its economic lifeline (thin as it is), China has considerable leverage over its "brotherly" communist neighbor.
Why isn't China then exercising this leverage? Beijing contends that it is quietly working on Pyongyang to see reason. And feels hurt that it is not getting the credit it deserves. Without Beijing's restraint, it is implied, things could get worse. In other words, Beijing indeed is contributing to regional stability through its tact and statesmanship. China is thus coming out in the region as a responsible power, a counterweight of sorts to US "brashness."