Ethnic Nepotism

An excellent description of ethnic nepotism from Steve Sailer:

The Iraqis' fierce resistance to foreigners (us) invading their country was predictable on any number of grounds. But perhaps the most interesting is the most fundamental: the theory of "ethnic nepotism." This explains the tendency of humans to favor members of their own racial group by postulating that all animals evolve toward being more altruistic toward kin in order to propagate more copies of their common genes.

Which doesn't mean that kin groups always cooperate—they also compete among themselves, in a sort of sibling rivalry writ large. But nepotistic solidarity still matters.

Even the notoriously fractious Afghan Pashtuns think in terms of: "I against my brother. My brother and I against my cousin. My cousin and we against the world."