The Jews of Europe, with no national home, perished, or fled to create one, in Israel. The Germans of the Baltic states, Prussia, Poland, Czechoslovakia, the Balkans and their own eastern provinces, almost to Berlin, were expelled in the most brutal act of ethnic cleansing in history -- 13 million to 15 million Germans, of whom 2 million perished in the exodus.

At the end of World War II, Europe's nations were more ethnically homogenous than they had ever been, at a horrendous cost in blood.

After 45 years of Cold War, the remaining multi-ethnic states -- the Soviet Union, Czechoslovakia and Yugoslavia -- broke up into more than two dozen nation-states, all rooted in ethnonationlism.

As Muller argues, ethnonationalism may be a precondition of liberal democracy. Only after all the tribes of Europe had their own ethnically homogenous nation-states did peace and comity come. And what happened in Europe in the 20th century may be a precursor of what is to come in Latin America, the Middle East, Africa and Asia.

In China, Uighurs, Mongolians and Tibetans all resist assimilation. Tatarstan may be the next problem for Russia. In the Balkans, it is Kosovo. Serbs there and in Bosnia may emulate the Albanians and secede.

Americans, writes Muller, "find ethnonationalism discomfiting both intellectually and morally. Social scientists go to great lengths to demonstrate that this is a product not of nature but of culture. ...

"But none of this will make ethnonationalism go away."

Indeed, we see it bubbling up from the Basque country of Spain, to Belgium, Bolivia, Baghdad and Beirut. Perhaps the wisest counsel for the United States may be to get out of the way of this elemental force. Rather than seek to halt the inexorable, we should seek to accommodate it and ameliorate its sometimes awful consequences.

And we should look to our own land. According to Pew Research, there will be 127 million Hispanics here by mid-century, tripling today's 45 million -- and almost 100 million new immigrants. No nation faces a graver threat from this resurgence of ethnonationalism than does our own.

Look homeward, America.