The writer is an associate professor at Dartmouth College and an associate fellow at Chatham House

Watchers of Japanese foreign policy become experts in nuance. We can talk at length about the legal distinction between “collective self-defence” and “collective security”. We can explain all the different words for “apology” used in Japanese leaders’ statements about the second world war.

After last week’s summit between Japan’s prime minister Yoshihide Suga and US president Joe Biden, we have new subtleties to scrutinise. In their summit joint statement, the leaders said: “We underscore the importance of peace and stability across the Taiwan Strait and encourage the peaceful resolution of cross-Strait issues.” It might seem innocuous, but the last time the allies mentioned Taiwan in a formal summit statement was in 1969. Now the question remains as to how far towards Taiwan’s defence Tokyo is willing to go.

A statement on Taiwan was proposed before Suga’s trip to Washington. American officials in particular wanted a response to growing Chinese pressure on Taiwan — the menacing rhetoric as well as last week’s incursion by a record number of Chinese military aircraft into Taiwan’s air defence zone. More broadly, as Suga said from the podium in the White House Rose Garden, “the regional security environment has become increasingly severe”.

Japan has long been reticent to discuss Taiwan with its US ally. Tokyo is skittish about the idea of collective security, with longstanding fears of being drawn into regional wars. Japan has sought to avoid antagonising China, now its largest trading partner. Suga’s willingness to talk about Taiwan represents a noticeable departure from a longstanding norm.

To Beijing, none of this appears subtle. China pervades the joint statement: its use of “economic and other forms of coercion”; its activities that are “inconsistent with the international rules-based order”; and its “unlawful maritime claims and activities in the South China Sea”.

Suga is the first foreign leader to visit the White House since Biden took office, signalling Japan’s (and China’s) centrality in American foreign policy. The visit follows the first ever summit of the Indo-Pacific “Quad” — an effort by the US, India, Japan and Australia to counter China. And the US-Japan joint statement was uttered just days after Biden announced the US withdrawal from Afghanistan, which will enable increased American focus on the Indo-Pacific. To Beijing, the message is loud and clear.

Whether much action will follow this message remains to be seen. It is unclear whether the Quad will have the military will and capacity to confront China. Some analysts advocate strengthening the Quad by co-ordinating defence and security policies, and engaging in exercises to improve military interoperability. Later this year, the Quad plans to hold its first in-person summit.

In the Rose Garden, Suga stated that “the deterrence and response capabilities of our alliance must be strengthened”. He’s right: China’s military build-up — notably in its massive naval and missile expansion — has transformed the military balance in Asia. Defense Secretary Lloyd Austin has ordered a review of the US military posture that could result in more American ships, troops and even long-range missiles in the region.

And what about Japan? The joint statement said that Japan has “resolved to bolster its own national defence capabilities” to further strengthen regional security. But the US has been prodding Japan to do precisely that for decades, and Japan — though watching an unfriendly neighbour building up a vast military in its backyard — has demurred.

Defending Japan, let alone supporting Taiwan, will require Tokyo to make non-subtle increases in defence spending. And it will require Japanese leaders to have a straight conversation with an unenthusiastic public who needs to decide how to answer a growing threat.