European history is full of dynastic marriages. A princess could expect to be married off to some foreign prince or king to cement an alliance (any of her own country she might marry would necessarily be either of inferior rank, or a close relative). AFAIK, this is not a feature of East Asian history. In Japan, certainly, it would have been unthinkable for the heir to the throne to marry a foreigner, though she were the eldest daughter by the chief wife of the emperor of China himself. Are there any examples of intermarriage between Asian royal families? If not, why the difference?
I don’t think it was all that different from Europe or the Near East, really. Japan is an odd case ( as in so many things ) due to its relative insularity. But even there political marriages were common internal to Japan.
In China, imperial princesses were certainly shipped off to foreign courts at times. Quoting:
The practice of reinforcing political alliances by marriages was to be followed by numerous Chinese or sinicized empires down to the Manchu period. Chinese princesses introduced into foreign countries the manners, customs, culture and luxury of China. Their presense in these countries justified the coming and going of embassies.
From A History of Chinese Civilization by Jacques Gernet, translated by J. R. Foster ( 1982, Cambridge University Press ).
So for example Gernet cites that the first significant diplomatic contact between Tibet and China was cemented by the marriage of a Chinese princess to a Tibetan ruler in 641 and she wasn’t the last. The T’ang in particular scattered brides to various nomadic groups on its borders as well to Tibet.
Certainly in central Asia the lineage of Chingiz Khan remained significant for centuries. My namesake leaned most heavily on the title ‘Gurgan’ ( he engraved it on coins ), indicative of his marriage to a Chagataid princess.
- Tamerlane
It depends on which period and how you define “foreigner”. During the 7th century, Japan was very chummy with the Korean kingdom of Baekje. Several Baekje nobles moved to Japan (especially after the kingdom’s fall) and the mother of Japanese emperor Kanmu (737-806), Takano no Niigasa was born in Japan to a Baekje family.
What about Southeast Asia? Were there royal marriages between, say, Burma, Thailand and Vietnam?
And India? Did rajahs typically marry the daughters of other rajahs, or kshatriya ladies from their own kingdoms, or who?
In India, marriage to form political alliances between kingdoms was a common enough practice (such as various Mughal emperors marrying women from the empire’s vassals). There’s also a lot of classical Indian literature where this happens (the play Manomani, the Mahabharta, etc.), so it must have been a common enough occurence.