Assessing the Scope of U.S. Security Commitments in Asia

The continued ascent of China is clearly making it more difficult for the United States to maintain its existing security commitments in Asia. But whether it soon will be too risky or too expensive for the United States to stay engaged in the region depends significantly on what forward-defensive line Washington draws. For many analysts, this would seem to be a new strategic question that the United States faces. One of the major contributions of Michael Green's authoritative and systematic examination of the U.S. approach to Asia is to show that this is, in fact, a very old question—one that U.S. presidents have struggled with for centuries and have derived very different answers to. Green's rich historical analysis helpfully sets the stage for considering the question of where the United States should now draw the defensive line in Asia.

By More Than Providence: Grand Strategy and American Power in the Asia Pacific Since 1783 carefully chronicles that even in just the post–World War II period, there has been a series of significant adjustments to the U.S. defensive line in Asia. It is important to recognize that these adjustments came in two forms that are analytically distinct and should be considered separately. The first are adjustments in the force posture and/or military strategy for safeguarding U.S. interests. Prominent examples include the Obama administration's "pivot" (which sought to shift more military assets to Asia) and Richard Nixon's Guam Doctrine (which aimed to reduce the U.S. forward military presence in the region).

The second, more fundamental kind of adjustment involves a change in the scope of U.S. security commitments in Asia. As Green recounts, "the Truman administration drew the American defensive line very deliberately between the offshore island chain and the continent, including Japan but excluding Korea—which the North then promptly attacked" (p. 8). He notes that George Kennan argued strenuously that no part of the Asian mainland was a vital U.S. interest, but that there was little support for the view that the United States should not intervene in Korea. After the Korean War ended, South Korea came under U.S. military protection. The United States' military footprint was later extended even farther into the continent during the Vietnam War. Green observes that Nixon was very receptive to Kennan's underlying viewpoint and sought "to limit American exposure on the continent of Asia, particularly after the bloodletting in Vietnam" (p. 339). Yet he notes that "whereas Kennan wanted the United States out of Korea in order to sustain a clearer maritime stance in the region and reduce the dangers of entrapment, Nixon was unwilling and unable to extricate the United States from the peninsula" (p. 340). After Nixon's decision to stand pat on the U.S. commitment to South Korea, no U.S. president has subsequently made any appreciable adjustment to the scope of the United States' security commitments in Asia (though Taiwan can be seen as a possible exception in light of the passage of the Taiwan Relations Act in 1979).

So where should the United States draw the defensive line in Asia now? Green does not outline his preferred formulation, but he correctly underscores that "the definition of the United States' forward defense line will become increasingly complex" (p. 545). As he notes, "the American forward presence in the Western Pacific is being challenged by China's military buildup and coercive claims to territories in the First Island Chain—and American strategists are debating whether the United States should be risking war over 'rocks' in the South China Sea, as one administration official put it in 2012" (p. 8).

Concerning the scope of U.S. security commitments, the United States would now seem to have four overall options. The first is to maintain the "status quo": to fully maintain the United States' roster of security commitments in the region on their existing terms. The second is to "do less": to pull back by cutting some or all U.S. security commitments. The third is to "do...