Three scenarios are possible. In the first, two regional powers — Japan and Indonesia — fill the vacuum left by the United States. In the second, ASEAN takes on a leadership role. The third scenario looks to China as the power most capable of filling the strategic vacuum. This third scenario is the most plausible — absent a strong US military presence, virtually all of Southeast Asia is likely to ‘bandwagon for profit’ with China.

US military retrenchment from Asia — where troops based in South Korea and Japan are withdrawn — is not implausible. Polls have indicated that many Americans believe the US should solve its problems at home before trying to solve those facing the world.

Capitalising on this theme of ‘America first’, presidential candidate Donald Trump threatened to withdraw troops from Asia and Europe if US allies did not pay more for their upkeep — though his line seems to have softened since becoming president. Major strategic thinkers have also called for a policy of restraint or offshore balancing, where the United States would only dispatch troops as severe threats emerge.

But without ‘boots on the ground’, the credibility of US commitments is likely to be questioned by Asian allies. Put another way, the US–Japan, US–South Korea, US–Philippines and US–Thailand alliances may continue to exist but will be considerably weakened. Similarly, strategic partnerships with countries such as Singapore, Malaysia, Indonesia and Vietnam are unlikely to be abrogated, but doubts will grow.

The first scenario that could emerge from a US withdrawal from East Asia is one where Japan and Indonesia make a bid to fill the strategic vacuum. Indonesia’s bid would be based on its status as the largest and most populous state in Southeast Asia.

But an Indonesian bid for leadership is unlikely to win the assent of the region. Indonesia does not possess the military or economic heft to entice support from other countries. Memories of the Sukarno years, where Indonesia sought to dominate the Malay Archipelago by force, would not be reassuring.

Japan has the military and economic heft to make a credible bid as the United States’ successor. Claims about its ability to provide regional public goods — economic and strategic — are also believable, and would feature in the calculations of Southeast Asian leaders. The legacy of World War II, with Japan having invaded and occupied many Southeast Asian countries, would be an obstacle.

Nevertheless, Japan seems to have only just woken up from its strategic slumber. Whatever regional initiatives it might advance are probably too little, too late. The one initiative on which it spent substantial political capital — the Trans-Pacific Partnership — was unceremoniously abrogated by the Trump administration. Japan seems to be lagging behind its main competitor, China.

Another possible scenario involves ASEAN taking the lead in forging a multilateral order. A troika of Indonesia, Vietnam and Singapore could play a lead role in streamlining and formalising the key norms governing intra-ASEAN relations. After 50 years of ASEAN diplomacy, a strategic order based on the absence of military conflict and the prevalence of rule- or norm-governed diplomacy is within reach.

The main challenge to this ASEAN-based strategic order is the role of external actors. Given the military absence of the United States, would China and Japan snicker at ASEAN’s claim to leadership of the region? Probably. Since a China–Japan condominium is unlikely, each country would prefer to call the shots itself, with each seeking strategic allegiances with Southeast Asian countries.

ASEAN member states would likely be faced with the dilemma of choosing between China and Japan in their respective bids to replace the United States. Japan’s historical baggage in Southeast Asia would make it an unlikely choice. Still, there is a slight possibility that both China and Japan would find an ASEAN-led strategic order convenient to avoid all-out strategic competition between themselves.

The most likely scenario: China fills the strategic vacuum left by a departing United States, with virtually all of Southeast Asia bandwagoning with China. Under this arrangement, the Southeast Asian strategic order would be underpinned by Chinese hard and soft power.

China’s hard power attributes — growing military might, the development of asymmetrical military strategies, and its use of economic carrots and sticks — are well understood. Its soft power attributes, however, are less well established. China’s soft power does not reside in Maoism or the numerous Confucius Institutes found around the world. It is to be found in its Belt and Road Initiative (BRI).

BRI is attractive to the region because it builds infrastructure where none yet exists and connects key markets in the East and the West, particularly Europe. Leveraging China’s post-1978 achievements in economic development, the BRI narrative harks back to China’s illustrious past, when it was at the height of its economic power. The implicit message is that BRI will come to fruition similarly to the ancient Silk Road, connecting China to Europe via land and the sea.

There are indeed formidable obstacles to BRI becoming a reality, not least because it trespasses through the backyards of two major powers, India and Russia. Yet, judging from the responses of most of the countries along the Belt and Road, the economic logic of the BRI seems irresistible. In return for opportunities to grow with China, however, Southeast Asia would likely accept China’s leadership and accommodate its key strategic interests. The future of Southeast Asia would look increasingly like a Chinese lake, analogous to the ‘American Lake’ conception of post-Monroe Doctrine Latin America.

Some Southeast Asian states with maritime disputes with China may find China’s ‘indisputable sovereignty’ trope disturbing. But even they, after doing the cost-benefit calculus, are likely to conclude that, absent the United States, they can or must live with a China-led strategic order. Strong economic growth means greater political legitimacy and that is something that most Southeast Asian governments understand.

Yuen Foong Khong is Lee Ka Shing Professor of Political Science at the Lee Kuan Yew School of Public Policy, National University of Singapore.

This article appeared in the most recent edition of East Asia Forum Quarterly, ‘Strategic diplomacy in Asia’.