China's Foreign Minister Wang Yi has sent his strongest warning to Japan, saying Japan's current leader has "crossed red lines by saying things that should never be said".

Why is this warning significant?

·First, this isn't coming from just any senior official. When Wang Yi, a former ambassador to Japan who knows the country inside and out, speaks this sharply, it underscores the seriousness of China's concerns.

·Second, this year is symbolic. Eighty years since China defeated Japanese aggression in World War II, this year is meant for historical reflection, not historical backsliding.

·Third, Wang Yi laid out China's determination in unmistakable terms. Japan hasn't shown any sense of responsibility so far, but Wang sent a clear message: Do not expect China to show any room for compromise on this issue.