So-called scientific racism is nonsense. On the other hand, the idea of identity based on common ancestry is powerful, unifying and non-falsifiable. It is the most common basis of nationalism.
The question is whether peace is possible in a world of nationalisms based on ancestry.
When nationalism is based on ancestry, a nation’s people are taught that they are like members of an extended family (usually a patriarchal family, headed by a father-figure) and that there is a bright line between members of the national family and all others.
Japan and Korea are two nations in which this idea is strong. Japanese mythology tells how the Japanese islands were created by the gods and their Emperor is the descendant of the sun goddess; Korean mythology tells how the Korean people were specifically created by the gods.
President Kennedy called the United States a nation of immigrants. Nobody would ever say that of Japan or the two Koreas. Nobody would ever call these nations multi-cultural.
The Han Chinese, probably the world’s most successful ethnic group, also have a strong sense of national unity. Unlike the Japanese and Koreans, they have a history of being able to absorb foreigners, including conquerors such as the Mongols and Manchus, through intermarriage and cultural assimilation.
The assimilation process is now going on, in a brutal way, with Tibetans and Uighurs. I think the reason the Vietnamese fear the Chinese more than they ever feared the French or us Americans is because of the real possibility that assimilation by the Chinese could end their existence as a nation.