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.
Japan was one of several countries that President Donald 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. Despite Trump’s reproach, 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. 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.
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 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, too. 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, South Korea can little afford to lose the United States’ defense support. It is instrumental in deterring military action from North Korea and in keeping Japan and China’s influence on the peninsula in check. With this history in mind, the Trump administration will try to outline clearer strategies with its Northeast Asian allies.