Victor Davis Hanson‘s latest column at National Review Online ponders the frightening notion that the United States might have reached a cultural tipping point.

Multicultural societies — from 19th-century Austria–Hungary to contemporary Iraq, Lebanon, the former Yugoslavia, and Rwanda — have a poor record of keeping the peace between competing tribes. They usually end up mired in nihilistic and endemic violence.

The only hope for history’s rare multiracial, multiethnic, and multireligious nations is to adopt a common culture, one that artificially suppresses the natural instinct of humans to identify first with their particular tribe. America, in the logical spirit of the Declaration of Independence and the Constitution, was exceptional among modern societies in slowly evolving from its original, largely European immigrant population to a 21st-century assimilated, integrated, and intermarried multiracial society, in which religious and racial affiliations were incidental, not essential, to one’s public character and identity.

But such a bold experiment was always tenuous and against the cruel grain of history, in which the hard work of centuries could be easily torn apart by the brief demagoguery of the moment. Unfortunately, President Obama, ever since he first appeared on the national political scene in 2008, has systematically adopted a rhetoric and an agenda that is predicated on dividing up the country according to tribal grievances, in hopes of recalibrating various factions into a majority grievance culture. In large part, he has succeeded politically. But in doing so he has nearly torn the country apart. Indeed, it is no exaggeration to suggest that no other recent president has offered such a level of polarizing and divisive racial bombast.