>But is there a non-circular way to approach the topic? I think there is, and once you do, you struggle to find evidence that China, Korea, and Japan have all that much in common culturally.

This borders on parody...

In the article, you didn’t see any mention of Confucianism’s influence. If we were to summarize the cultural similarities of these East Asian countries, they all belong to the Confucian cultural circle. Confucianism is not a religion in the strict sense like Christianity, Buddhism, Islam, Shintoism, etc. It emphasizes family, education, and ritual (not the politeness of ritual, but a larger concept that is more like a set of rules to maintain stability). Although we may recite some excerpts from the Analects when we go to school, most people don’t care. However, Confucian thought has been deeply ingrained in all aspects of life for thousands of years