On a recent trip to the Pacific, US Defense Secretary James Mattis reaffirmed the United States’ commitment to guard Japan against foreign threats. Both the US and Japan have interests in the South China Sea. Geopolitical expert George Friedman has written extensively about this shared interest in This Week in Geopolitics (subscribe here for free).

However, overlapping interests are not the same as identical interests. The US and Japan both want to protect sea lanes in the Pacific. But the motivations driving each country’s national strategy differ. Japan’s greater dependency on imports across sea lanes and proximity to China make events in the South China Sea a greater threat for Japan than the US.

 

tpsdave / Pixabay

China’s aggressive posturing in the South China Sea is primarily designed for domestic consumption by stirring up national pride to legitimize the regime. Japan perceives these moves as serious threats. Japan must import nearly all the oil and raw materials to function economically and militarily.

Japan’s Biggest Weakness

Japan is an island nation and must have all of its imports transported via maritime trade routes. Thus, it is imperative for Japan’s survival to maintain open access to South China Sea shipping lanes.

The US is the dominant naval power in the Pacific and grants Japan freedom of movement in the South China Sea. The current arrangement works, but it means Japan is dependent on its relationship with the US to import required materials.

Oil is one of Japan’s greatest vulnerabilities. According to a study by British Petroleum, Japan consumes an average of 4.15 million barrels of oil per day. It has an estimated 500–600 million barrels in strategic reserves. This is further bolstered by an agreement with South Korea to share oil reserves in an emergency. South Korea’s 81-million-barrel reserves would give Japan extra time in a blockade or war.

On its own, Japan only has enough oil in reserve to last for about four months. In a best-case scenario, if South Korea were to give Japan all of its oil, it would only provide Japan an additional three weeks’ worth of reserves.

However, in such an emergency, it is unlikely that South Korea would grant Japan access to all of its oil reserves. This makes Japan hyper-vigilant toward any Chinese threat to block sea lanes. Cutting off oil from Japan is an existential threat. It’s the same one that drew Japan into the Pacific war with the US.

United States’ Interests

On the other hand, the US’s primary concern in the Pacific is preventing the rise of a single state that could upset the regional order. A regional hegemony challenging US naval supremacy is a threat.

China has the largest economy and is pouring money into increasing military capabilities. That makes it the greatest threat to existing regional balance. While this distribution of power is constantly in flux, China remains the power the US must balance.

The US has guaranteed the defense of Pacific countries including Japan, the Philippines, and Taiwan since World War II. It uses this interwoven web of alliances to balance China’s challenge.

The US government is concerned with its allies’ defense not because of moral benevolence—but because those countries play a critical role in the US’s balance-of-power strategy.

China’s Motivations

Understanding Japanese fears requires knowing China’s motivations in the South China Sea. China also needs access to maritime trade routes, but unlike Japan, China is more concerned with its ability to export goods than importing them.

China is afraid of being boxed in by the US and its regional allies. Those include Japan and the Philippines, which could block China’s access to Pacific sea lanes. This mentality encourages its offensive posturing. By building artificial Pacific islands, China is trying to secure additional territory to increase its area denial capabilities. That would make any potential attack more difficult.

China’s regional interests place it in direct conflict with those of Japan. China is not currently ready for a real fight with either Japan or the US, but its threats are felt more acutely by its nearby neighbor than by the US.

US Concern

Mattis’s recent remarks do indicate US concern about Chinese aggression and territorial claims in the South China Sea. But the US’s concern is more for Japan and other regional allies than its own economic or military interests.

Mattis’s remarks show what the US would view as a red line for Chinese activity in the Pacific. Japan would prefer that the US enforce this line on all Chinese activity in this region.

From the US’s perspective China’s pursuit of the islands and activity in the region thus far are not serious enough to respond with anything but posturing. China does not have an interest in provoking a war. But Japan must base its national defense strategy on what is possible even if unlikely. This dynamic has defined the geopolitics of the Asia-Pacific region for over a century. It is important to be precise about both US-Japanese shared interests as well as gaps between them.