Almost a decade ago, a military conflict between the United States and its allies on one side and China on the other was described by major foreign policy and defence observers as the "unthinkable war." Lately, it's become clear that those same experts are now thinking through the unthinkable. After the recent G7 summit in Hiroshima, Japan, Beijing summoned Japan's ambassador to China to complain about what it called the "anti-China" tone of the summit. Later, the Chinese government publicly berated Great Britain. On the second day of the G7 meeting, the assembled leaders issued a joint communique that singled...