In a Taiwan war, the US could find itself fighting China without its top allies

• The US military may be forced to confront a Chinese invasion of Taiwan without top allies.
• Japan, Australia, the UK and Canada are likely to provide no military forces to counter China.
• RAND Corp. analysts said these "middle powers" could help in other ways, however.

If the US decides to defend Taiwan from Chinese invasion, it may have to do so alone.

Several of America's biggest allies are unlikely to commit troops to save Taiwan, either because they lack the military capability or don't want to risk all-out war with an increasingly formidable China, according to a new report by the RAND Corp..

For Japan, Australia, the UK and Canada, aid "would be confined to diplomatic support for Taiwan and endorsement of likely US sanctions on China," concluded RAND, an American think tank, which surveyed experts in the four nations . If this proves right, it means that any military response to a Chinese invasion would be limited to American forces.

"Our respondents believe that the US will receive logistics and materiel support from other countries, but its forces will have to go it alone in responding to an invasion by China," Rafiq Dossani, a RAND senior economist who co-authored the study, told Business Insider. However, there was more support in Japan and Australia to commit their navies to assisting an American-led effort to break a Chinese blockade of Taiwan.

That Canada, for example, might not be able or eager to rush to Taiwan's defense isn't a surprise. But for Japan, whose security would be gravely affected by a Chinese takeover of Taiwan, the issue is more complicated.

"Despite its military power, commitment to the region, and US backing, Japanese pacifism (both popular and constitutional) and the fear of a retaliatory attack by China are likely to limit Japan's military support for Taiwan , perhaps only to logistics and supplies," RAND said. "Any support that they would offer to a US-led military response would likely be limited to logistics and materiel support."

The goal of the RAND study, which was sponsored by Taiwan's Ministry of Foreign Affairs, was to examine how America's medium-sized allies may deter or mediate a conflict between China and Taiwan , a democratic island that China's communist leaders consider a breakaway province. The US is highly dependent on its regional allies like South Korea and Japan for basing, but the prospect it would have to fight without their ships and troops against what's likely to be a larger Chinese force may tarnish its deterrent power.

Researchers classified Japan, Australia, the UK and Canada as "middle powers," which RAND defined as nations "that are not small but lack the sheer size and influence to significantly disrupt the global order." The study excluded nations that already faced a risk of direct conflict with China, the US and their respective allies. India and South Korea were also excluded "because those countries have declared that they will not play a mediating role in a cross-Strait conflict."

RAND sent questionnaires to 49 diplomats, defense officials, policy analysts, business executives, journalists and legislators in the four nations. The various responses shared "remarkably common" views about a China-Taiwan war .

What is especially striking is the pessimistic self-image. The British experts, for example, felt that "the UK's distant location and weak military assets, in addition to its trade dependence on China, lead to limited UK interest in defending Taiwan militarily."

Nor do the four US allies believe that Beijing fears them enough to refrain from attacking Taiwan . "Our respondents thought that China views these four middle-power countries as too weak militarily to take on China on their own and as marginal players in a US-led coalition," the report found.

On the other hand, America's top allies don't share American fears that a massive Chinese military buildup and Chinese leader Xi Jinping's avowed determination to "reunify" Taiwan with China are steps toward war, but rather may be nationalistic posturing. "According to our respondents, China's main goal is to legitimize its current domestic political system (i.e., the rule of the Chinese Communist Party)," the report said. "To accomplish this goal, China must be seen within as a great power, preeminent in Asia, and able to achieve high economic growth. An invasion of Taiwan would jeopardize such perceptions and thus be deemed an unacceptable risk relative to the status quo."

Taiwan's military is not inconsequential, with nearly 200,000 active-duty soldiers, anti-ship missiles and mines , and soon F-16 fighters and submarines. But this is a fraction of China's military might, and Taiwan would probably need outside assistance to repel an invasion or break a blockade . While the US would provide the bulk of such a relief effort, allied contributions would be vital, as would unfettered use of bases in Japan and Australia.

To American hardliners already resentful that some NATO nations aren't spending enough to defend Europe, the reluctance of its allies may smack of cowardice, and stick the US with the burden of Pacific security. But this may also reflect military and geographic reality. Canada's small military could muster only a token force for Taiwan's defense. Britain's shrinking armed forces, which already have European commitments, would struggle just to dispatch a small carrier task force 6,000 miles to the South China Sea .

Though Australia is a Pacific nation, and has diesel-electric submarines and F-35 stealth fighters, it still lacks the ability to project and sustain military operations 5,000 miles away in Taiwan.

But the biggest question mark is Japan: Okinawa is about 500 miles from Taiwan, Japan has territorial disputes with China over various islands in the East China Sea, and the Japanese military is rated among the 10 most powerful in the world. Furthermore, Japan's territory and the US military bases it hosts will be essential to any US effort to counter China.

Yet if Japan, Australia, Britain and Canada are reluctant to confront China, there are actions they can take to help Taiwan. RAND recommends that they create a joint plan for trade sanctions to deter China from attacking Taiwan. In addition, the four middle powers could play a role in mediators to prevent a Taiwan war from happening.

"Indeed, middle powers might be the only ones that can play a mediating role in such a conflict if tensions between the great powers were to escalate," the study noted. "However, as of this report's writing, no middle power has enough influence over both great powers to play such a role, even in coalition with other middle powers."

Which means these middle-ranked nations need to build up their capabilities, military and otherwise. "To build credibility with both great powers, the four middle powers need to rebuild and bolster their strategic autonomy, material power, and commitment to the Asia-Pacific region."

The study also implicitly raises questions about how much the US can count on its NATO allies for support outside Europe. While NATO nations did send small contingents during the Afghan war, confronting China is different.

"I think that NATO should take seriously the possibility of European middle powers preferring not to be involved in a conflict in which their adversary does not directly threaten their national security," Dossani said."

Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds an MA in political science from Rutgers Univ. Follow him on Twitter and LinkedIn .