The Gada system organizes Oromo men into generation classes that move together through a fixed sequence of grades over roughly forty years, from childhood and herding through warfare and into government, before passing into the ranks of elders whose counsel still carries weight. One class at a time, the Luba grade, holds executive authority for a single eight year term, electing a chairperson known as the abba gada along with officials and an assembly, before handing power to the class behind it.
That handover is not a formality. Gada assemblies, above all the gathering held at Gumii Gaayoo, make law, judge disputes and can depose an abba gada who governs badly, a check UNESCO's own inscription calls a rare indigenous constitutional order rather than a monarchy. Oral historians transmit the system's history, law and rules of conduct, and women participate directly in decisions protecting women's rights, even though the classes pass through the male line.
The system is religious as much as political. It sits within Waaqeffanna, the Oromo religion centered on the sky god Waaqa, and its most visible expression is Irreecha, a thanksgiving festival held as the rainy season ends at rivers and lakes across Oromo country. Participants carry fresh grass and flowers to the water in thanks for the season, and since the early 1990s the gathering at Hora Arsadi near Bishoftu has drawn crowds large enough to make Irreecha one of the most visible religious festivals in the Horn of Africa.
Ethiopian imperial conquest in the late nineteenth century suppressed Gada governance for a century, and it survives today among the Borana Oromo of Ethiopia and northern Kenya. UNESCO inscribed the Gada system on the Representative List of the Intangible Cultural Heritage of Humanity in 2016.