Renard Sexton, in the 538 blog, has addressed an issue I wrote about here, which is the effect that Japan's rejection of their long-time ruling party, the Liberal Democratic Party, will have on that country's close alliance with the U.S.
Sexton cites trade data that show that China has overtaken the U.S. as Japan's largest trading partner. I agree with him that such a shift affects the political, as well as economic, relationship between countries.
But, I think he overstates the effect that might have in terms of weakening the military alliance.
Since 1954, Japan has maintained what it euphemistically calls Self-Defense Forces. Those forces constitute quite a large military. However, it is small in comparison to Japan's large population and GDP. It would be difficult to reconcile a full-size military establishment with the country's promise in its post-World War II constitution to abandon militarism.
Japan has largely relied on American military protection. If it were to substantially shift away from its alliance with the U.S., Japan would need to either fully remilitarize, or find itself a new strategic partner(s).
Toward the end of his post, Sexton mentions the historically strained relations Japan has had with some of its Asian neighbors, stemming from Japanese aggression against those countries during and before World War II. While that has not stopped those countries from building up a significant trading relationship with Japan, emotions still run high, regarding that troubled history. If Sexton thinks that closer relationships with Japan's Asian and Oceanic neighbors (Greater East Asia Co-Prosperity Sphere, anyone?) can substitute for its American alliance, he's taking insufficient account of history.
I think there will continue to be gradual and incremental changes in East Asian power relationships, but I don't expect any sudden and dramatic shift.