>Humans definitely have the "my team vs your team" mentality. Studies show that having a rival or hatred towards another group (political party, sports team, etc) it actually stimulates the same parts of the brain one would have when they achieve something purposeful in their lives.

urgh i have noticed this.

try pointing out that on economic issues both parties in most western nations are near-identical (pro-corporate neo-liberals) and you see it immediately.