Triblism developed out of actual tribes and the need to defend your family - since you were likely related to everyone in the tribe. It's also evolutionary and helps protect your genes. Those early tribes would eventually evolve into societies that lived in larger towns and cities. This has developed into nationalism on a larger scale. Also, things within our lives that we think are benign might not be. Students yelling to kill or crush the other team at college sporting events, for example.
- Chris Webster