How much of Japan's traditional culture comes from China ?

[bossel]

Really ? The Mongols and Manchu only came in the 14th and 17th centuries. That's not "ancient history".

but

If you study Chinese history, you can find that some different ethnic people ruled China by turns.

Actually, Kaerupop is quite right. Your view falls a bit short of the truth, Maciamo. A lot of ethnicities ruled China, some Chinese (you forgot that there are different Chinese ethnicities), some foreign. The Mongols were not the 1st foreign rulers in China, though perhaps the 1st who ruled all of it (don't really remember). Esp. in Northern China (during the time of South-North division) you have quite a number of foreign rulers.

There are other foreign influences as well, eg. during Tang there were a number of high officials of Turk origin.

I don't know, whether Kaerupop thought of this, when he wrote the above, but if you include Chinese ethnicities other than Han, you'll get even more varying influences.

Korean like German.

Er..., I think, your linguistic comparisons are limping a bit.