"The culture of the umbaru of the lower Teganze is fascinating and perplexing to those hailing from more civilized walks of life. For instance, the Tribe of the Five Hills frequently engages in tribal warfare with both the Clan of the Seven Stones and the Tribe of the Clouded Valley, but these are matters of ritual and not of conquest. I had heard tales that these wars are waged in order that the victors may replenish their supply of raw materials for the human sacrifices that their civilization revolves around, and when I timidly asked my hosts more about this topic, I must admit their laughter made me fear for my safety. However, through stumbled attempts at communication of such complex topics as what constitutes heroism and honor in their society, I gathered that only those taken in battle are considered worthy of the ritual sacrifice, much to my relief."— Abd al-Hazir(src)
"To live is to sacrifice. To sacrifice is to live."— A mantra associated with the harvest(src)
The Igani Bawe is traditionally held in the interval between seasons. It always commences at sunrise, and ends at sundown. The purpose of the Igani is not to slay their fellow Umbaru on the battle itself (this is considered taboo), but rather incapacitate them and capture them to be sacrificed afterwards. When an Umbaru is captured, they embark on the Te Wok Nu'cha, the Final March. When they are sacrificed, their bodies are smeared in ritual oils before their blood and organs (the latter of which is placed in jars) are offered to the spirits of the Unformed Land. The Umbaru believe that by doing this, they not only nourish the realm for those who will enter it later, but also strengthen their own world (e.g. allowing healthy crops to grow and the seasons to pass). Most Umbaru are prohibited from entering the Ghost Trance during the Igani, as the high priests state it disorientes the souls of the recently sacrificed tributes.
In truth however, the Igani Bawe is unnecessary. Mbwiru Eikura exists regardless of whatever sacrifices the Umbaru make, but it is not utopia either. Two Witch Doctors discovered the truth, Nazeebo and Benu. While the former ended up following the Fallen Star to New Tristram, Benu, who became a spirit, sought to guide the Umbaru away from the needless warfare that they undertook.