The move led to a fierce confrontation between Chinese and Vietnamese government vessels and saw relations between the two countries deteriorate to their lowest point since 1988. The standoff also served as a litmus test to identify who will side with whom in this conflict. While most of the world remained neutral, several states came out in support of Vietnam in one form or another. Among these supporters, the United States and Japan stood out as the most powerful and staunchest.

The United States stands out among outside stakeholders to the South China Sea (SCS) with its intense interest in the region. Since 2010, American leaders have repeatedly declared that Washington has a “strong national interest” in freedom of navigation and a “strong interest” in the peaceful and lawful settlement of the disputes there. Both the U.S. economy and U.S. global power and regional primacy in the Asia-Pacific depend to various extents on freedom and peace in the waterways running through the SCS.

In fact, the impact of a blockade in the SCS on the U.S. economy would be significant but not extremely high. Less tangible but more important is the role of the SCS for U.S. global power. U.S. naval supremacy in the Western Pacific, of which the SCS is a critical part, is a key to its regional primacy in the Indo-Pacific, which in turn is a major pillar undergirding the U.S.-led liberal world order. Important as it is, this link from the SCS to U.S. interests is not direct and not very visible and tangible. This fact makes it harder to convince the American public of the significance of the SCS to their interests.

American commitment to the SCS is limited by the U.S. need for breathing space after two expensive wars and a severe economic crisis. China has acted to take advantage of this virtual power vacuum, intensifying its revisionist actions in the region. However, as those revisionist actions become more visible to the American public, U.S. commitment to this critical region may once again strengthen.

Japan’s interests in the SCS derive primarily from its dependence on the waterways there and its preference for a U.S.-led regional order. If China dominates this chokepoint, it will be able to switch off at will about 60 percent of Japan’s energy supplies, and it will likely replace the United States as the sponsor and leader of a new regional order. A Chinese-led regional order will most likely be far less liberal and favorable to Japan than the current U.S.-led order. Japan thus shares with both the United States and Vietnam a strong interest in maintaining the status quo in the region. What role can Japan play in maintaining stability in the SCS?

First, Japan – and the United States, for that matter – is ill-suited to act as an honest broker to the dispute. The honest broker must be trusted as such by both sides of the dispute, and Japan hardly fits that bill with China, particularly given its own dispute with China in the East China Sea.

Second, Japan is unable to play the role of an external deterrent. Lacking nuclear weapons and perhaps more dependent on China economically than vice versa, Japan is simply unable to deter China in general.

Balancing, therefore, remains the only possible role for Japan to play. Japan is willing to support Vietnam against China, as evidenced by Tokyo's provision of coast guard ships as gifts to Vietnam during its oilrig crisis with China recently.  But does Japan, even when joining forces with Vietnam, have the capacity to balance China? This is an interesting question that needs more study, but a look at the combined military and economic power of the two suggests that they cannot. China possesses several key advantages over a Japan-Vietnam coalition, most obviously its nuclear weapons and its central role in Asia’s economy.

The most effective role for Japan to play in the SCS is to facilitate a coalition with the United States, Vietnam, the Philippines, and other countries that share a common interest in maintaining the status quo. Only a U.S.-led coalition can balance Chinese power in the region. Given its high stakes in the SCS – and the perception of those stakes by its elites – Japan is likely to be willing to play this role. But there is an issue with the coalition leader: With its geographic and psychological distance to the SCS, Washington may be the least willing among this coalition’s members. This may be a factor that prevents the coalition from unilaterally escalating the conflict, but it may also be a factor that encourages China to underestimate the resolve of its rivals and become dangerously provocative.

That in turn suggests the potential for a new era of instability and tension in the SCS, with each stakeholder playing their own role.