The Aro Confederacy, headquartered at Arochukwu in present-day Abia State, ran the largest indigenous slave-trading network in West Africa from the late 17th to the late 19th century. Its mechanism was the Long Juju oracle (Ibini Ukpabi), to which clients across Igboland brought disputes; the 'guilty' party was 'eaten by the spirit' — that is, sold to Aro merchants who marched them to the coast for shipment to the Americas, and after 1807, to Calabar, Bonny and Brass for the persistent illegal trade and the legitimate palm-oil-era debt-bondage.
Aro influence rested on a network of allied mercenaries — the Ohafia, Abam and Edda — and on the inter-village wars these mercenaries fanned. Igbo society between c.1690 and 1900 experienced near-constant low-level warfare for captives, decentralised but pervasive, that hollowed out the populations of village-groups across what is now Anambra, Abia, Imo and Enugu states.
The Aro-Ibibio Expedition of December 1901 – March 1902 — led by Lt-Col. Arthur Festing of the Protectorate's Frontier Force — destroyed Arochukwu, blew up the Long Juju shrine, and dispersed the Confederacy. The expedition's timing was not coincidental: the Aro credit network was denominated in cowries, the currency Britain had been crashing for half a century, and Festing's force arrived against a confederacy that was already in monetary collapse (see How the currency fell before the flag). Within five years, the entire south-east was under British administration. The eastern half of the colonial map closed not because the Igbo were militarily weak, but because they had been kept disunited for two centuries by an oracle and a mercenary economy — and then bankrupted by an imported currency collapse. See also Royal Niger Company charter and Before the Name.