Explain how tribalism is depicted in Chimamanda Ngozi Adichie's half of a yellow sun

As depicted in Half of a Yellow Sun, the war that Biafra wages against the North has a few different objectives. The hostilities are naturally tinged by righteous anger over the massacres that occurred after the first coup. There is also, though, a more optimistic side to the uprising that divides Nigeria in two: the desire to form a nation that is secure from ethnic violence and that is an example of enlightened patriotism. Though this desire is promoted by several thoughtful, assertive characters - Odenigbo, Kainene, Olanna, and Richard among them - such dreams of a flourishing and independent Biafra collapse. Military and economic deficiencies explain part, but not all, of the futility of Biafra's aspirations. Instead of bringing out the best in Adichie's characters, war reduces them to depressed shells of their former selves (in the case of Odenigbo) or pressures them into committing acts of violence (in the case of Ugwu, who rapes a bar girl) that cut against the fledgling country's lofty ideals. It is perhaps no coincidence that the book begins and ends in Nsukka, using the recurrence of this location to suggest that war creates a vicious circle - at best looping characters back to exactly where they were, just sadder, poorer, and angrier than they were before.