Psychology
Social Identity Theory and Intergroup Conflict
Quick fact
Henri Tajfel's minimal group experiments showed that even arbitrary group assignments (e.g., based on dot estimation) lead people to favor their own group over others, demonstrating that intergroup bias can form without any history of conflict.
Why this is interesting
Have you ever felt a stronger connection to your sports team than to your own family? Why do we so easily form 'us vs. them' mentalities, even in casual settings?