What is the ethnic group of Northeast Asia?

Northern China, Korea, and Japan all appear to be of the same ethnicity as opposed to Southeast Asia. Whenever I try to look it up online I just get answers that are lingo-political, such as Chinese, Korean, Japanese, etc. Take away the borders and these are all the same people right?

I think many folks would tell you that they see differences in the physical appearance of the three populations, suggesting that the groups are not the same. Indeed, it seems as though the three (Chinese, Korean, and Japanese) do have different ancient ethnic roots, as follows:

Japanese - descended from the Jomon (native to Japan) and Yayoi (which may include some Korean or Chinese blood)

Chinese (Han) - descended from the Huaxia (from around the Hwang Ho/Yellow River)

Korean - descended from Altaic-Siberians (similar to Turkic and Mongolian groups)

It's not just lingo-political. And, needless to say, the groups see their own cultures as very distinct from one another.

they don't look the same at all

There's the Altaic Asian(Korean and Japanese) and then there's the Silotic(Chinese. They're very different in looks and culture

Hans are probably the majority.

East Asian

Korean and Japanese are Altaic from Middle Asia.

Also, linguistically, Korean and Japanese have almost same grammar structure even though they have own characters. Besides, Chinese are totally different from them.

eg:

Korean, Japanese = Subject + Object + Verb,

Chinese = Subject + Verb + Object.

- Siberian, Manchurian, Mongolian, Korean, Japanese belong to the Altaic group.

- Chinese, Tibetan, Thailander, Vietnamese, Myamese and other south east Asians belong to the same ethnic/linguistic group.