Terms like “tribalism” and “sectarianism” here underscore a crucial reality: the attitudes and emotions in highly polarised contexts like the US are not specific to those contexts. They emerge whenever intense intergroup conflict maps onto social identities such as partisanship, ideology, religion, sect, ethnicity, region, or tribe. That is, while every group rationalises their fear and hatred of the outgroup by pointing to its specific crimes, the emotions are strikingly similar and symmetrical across radically different conflicts, whether between Protestants and Catholics, Hutus and Tutsis, or Sunnis and Shias. This pattern is typically explained in terms of our evolved “tribal” or “coalitional” nature. Our species was forged under selection pressures that favoured powerful motives and abilities for forming alliances designed to outcompete other alliances for prestige, dominance, and resources. So, when we support and identify with a group, automatic “coalitional instincts” are activated. We divide the world into ingroup and outgroup, us and them. We frame group relations as zero-sum conflict for power and esteem. We become obsessed with sending and monitoring signals of group loyalty. And we become instinctive apparatchiks and propagandists, embracing narratives crafted to make our side and its defining narratives look good, and the other side look bad, if not outright demonic. Polarisation exacerbates those instincts, which in turn exacerbate polarisation, fuelling a runaway process in which competing tribes lose access to a shared reality and a willingness to empathise and compromise with each other. (View Highlight)