When did Japan emerge as a nation?

In Japan. February 11th is National Foundation Day.
This date is based on legends chronicled in the ancient Kojiki and Nihon shoki texts, but from an academic perspective, there is doubt over the historical accuracy.
Since Japan has no written records earlier than the fifth century, we can probably learn more from Chinese texts.
According to the Chinese text Gokanjo(History of the Later Han Dynasty), in the year 57 A.D. the king of the Japanese kingdom of Na dispatched a mission (to China), while "The Account of the Wa People" in the Wei zhi (The Wei Chronicle) contains a reference to a queen named Himiko in the land of Yamatai, who ruled over about 30 countries.
Although the Nihon shoki regards Himiko as Empress Jingu, historians dispute this claim.
It could be that following the decline of Yamatai rule. by the seventh century the country was unified into one polity. which then served as the basis for Yamato rule.