Mattis' trip to Japan and South Korea, the United States' most important allies in Asia, is meant to reaffirm Washington's commitment to the countries at a time of growing regional uncertainty. China's economic rise and quick progress in turning its wealth into military power have set off a new round of competition in the South and East China seas. And in the process, Beijing has upset the strategic order that has prevailed in East Asia since the end of the Cold War. Though Trump has yet to lay out his foreign policy strategy toward China, recent comments from the president and his staff suggest that the administration considers China a major threat to U.S. interests in Asia and around the world. This view doubtless influenced the administration's decision to send Mattis to Japan and South Korea, countries that will play a central role in the United States' efforts to constrain, or militarily contain, China.
But China is not the only reason for Mattis' trip. As important as Washington's relationships with Seoul and Tokyo are, they are also sensitive to changes in regional dynamics, politics and public opinion — not only in South Korea and Japan but also in the United States. Unless they are properly addressed, the inherent complexities of these partnerships could undermine them, preventing the United States and its allies from mounting a concerted response to long-term strategic threats such as China or North Korea.
A Mutually Beneficial Arrangement
The United States' partnership with Japan is a legacy of Washington's efforts to contain the spread of communism in Asia during the Cold War. Since then, Japan has hosted U.S. troops on its soil, and today, roughly 54,000 American military personnel are stationed on the Japanese islands. This is a mutually beneficial arrangement for Tokyo and Washington, at once strengthening Japan's self-defense capabilities and enabling the United States to project its military power, and particularly its unrivaled maritime prowess, in the region.
During the race for the U.S. presidency, the terms of the alliance came under fire. Japan was one of several countries that Trump accused of taking advantage of the U.S. security umbrella. He also criticized Tokyo for not paying its fair share for the tens of thousands of U.S. troops stationed in Japan, as well as their 42,000 dependents. (In reality, Tokyo covers about 42 percent of the cost of maintaining U.S. bases in Japan, a far greater share than most NATO members pay for U.S. military installations in their borders.) Despite Trump's reproach, however — and the periodic public outcry in Japan over the U.S. military presence in the country — each side has powerful incentives to continue the alliance. U.S. support provides Japan with a level of protection that enables Tokyo to play a more proactive role in maintaining security and countering China's sway in the region. Tokyo's assertiveness, in turn, relieves the pressure on Washington to compete directly with Beijing for influence in regional groups such as the Association of Southeast Asian Nations. The United States' military bases on the Japanese islands, meanwhile, offer a staging ground for maritime operations that would be invaluable in the event of a protracted military conflict with China.
The U.S.-South Korea Alliance: It's Complicated
By contrast, the United States' partnership with South Korea, another holdover from the Cold War era, is focused on a single objective: to secure the Korean Peninsula. The United States' bases in the country do not provide the same strategic advantages that its installations in Japan do since most of them are located inland. In addition, many people in South Korea vehemently oppose the presence of U.S. forces within their borders, and Trump has accused Seoul, like Tokyo, of not paying its share of the cost for Washington's bases. These factors, combined with South Korea's political upheaval, its greater economic reliance on China and its strained relationship with Japan, cast doubt on the future of Washington's alliance with Seoul.
Still, the United States has good reason to keep close defense ties with South Korea. Beyond its desire to maintain stability along the border with North Korea, Washington has an interest in sustaining its alliance with Seoul to keep Beijing at bay. As South Korea enters a period of perhaps prolonged political and economic turmoil, China could take the opportunity to forge closer ties with its neighbor across the Yellow Sea. South Korea, similarly, can little afford to lose the United States' defense support, which is instrumental in deterring military action from North Korea and in keeping Japan's and China's influence on the peninsula in check.
These considerations likely guided Mattis' decision to make South Korea and Japan his first destinations as secretary of defense, and they will help determine his goals for this trip and future trips to the region. Mattis' focus for the time being will be on reassuring his counterparts in Seoul and Tokyo that the United States intends to uphold its security commitments. And in time, the Trump administration will try to outline clearer strategies with its Northeast Asian allies for managing the threats that North Korea and China pose. If Trump's comments are any indication, these strategies will probably be very different from those his predecessors have pursued.