Because mankind has a deep yearning for a sense of belonging and for leadership, humans naturally form groups with established leaders. Some groups are positive manifestations of collaboration and solidarity among individuals. But when groups are based on an ideology or a particular tribe, they can become discriminatory and oppressive toward non-members, especially if a domineering, charismatic leader is in charge. The emergence of populist and nationalist movements in the United States, the United Kingdom, France, and other European countries suggests that tribalism is on the rise in the West. By Sami Mahroum.