Australia's isolation gives it a vast buffer against military threats, granting it free rein in its near abroad, along with considerable wealth and stability. At the same time, because Canberra lacks the resources to sustain a globally capable navy of its own, it has tried to prove its value to maritime powers capable of securing critical sea-lanes on its behalf. To that end, Australia has routinely participated in U.S.-led military operations of marginal relevance to its interests. But the new U.S. administration's apparent ambivalence toward traditional alliance networks and its possible willingness to force a confrontation with Beijing have cast doubt on the future of the established economic and security architecture of the Western Pacific.

Australia's underlying imperatives have not changed. Isolationism is not an option, and the United States is the only maritime power it can rely on to guarantee the security of the seas. But the shifts underway in Washington and the Western Pacific are forcing Canberra to consider how to secure its interests and assume greater responsibility for regional peace and prosperity.

Throughout its history, Australia has toyed with decreasing its reliance on U.S. security guarantees in pursuit of firmer partnerships with Asian powers such as China. After all, China has a greater economic incentive to sustain Australia's national security than the United States does. Nonetheless, Canberra has stayed a firm U.S. ally, in part because the United States is still the only global naval power. Australia also seems to believe that the United States will eventually return to its traditional postwar role in the Western Pacific.

Until then, though, Canberra will prepare for a wide range of possibilities in Washington's foreign policy toward the region — from disinterest in established alliance structures to hawkish moves to constrain China. For the Australian government, this means investing heavily in its own forces (the 2016 defense white paper outlined a $26 billion jump in annual defense spending over the next decade).

On regional security issues, however, Australia may respond to uncertainty with even greater circumspection. The country will refrain from taking any action that might nudge the region closer to a showdown. Australia will also be hesitant to elevate defense cooperation with countries such as Japan to the level of a formal alliance, which would tie its security fate to flashpoints in Northeast Asia. It will even extend this cautious approach to defense cooperation with the United States; Canberra has so far resisted U.S. pressure to conduct freedom of navigation operations in the South China Sea. Though Australia will not deviate from its alliance with the United States, it has little choice but to find ways to engage the changing region on its own terms.