The Aro Confederacy (Igbo: Otu Aro, 'the Aro alliance') was the commercial state-within-a-state that dominated the slave-export and palm-oil trade of the Bight of Biafra between roughly 1690 and 1902. Its capital was Arochukwu in present-day Abia State, where the Ibini Ukpabi oracle — known to Europeans as the 'Long Juju' — was housed in a sacred grove of caves and waterfalls. The oracle, attended by Aro priests, adjudicated disputes from across Igboland, the Ibibio, Efik, Ogoni and Ekoi peoples; communities sent delegations on long ritual journeys to consult it.
The genius — and the horror — of the Aro system was that those judged guilty by the oracle were said to have been 'eaten' by the deity. In reality they were sold by Aro middlemen down the slave routes to Bonny, Calabar and Opobo, where Liverpool and Bristol slavers shipped them across the Atlantic. The Aro maintained more than 150 settlements (Ndi Mgborogwu) across Igboland, each headed by an Aro merchant family, which served as collection points for slaves obtained either by oracle judgment, by raids organised by allied Abam mercenaries, or by purchase in local markets.
The Aro never built a centralised state. The confederacy was governed by the Eze Aro at Arochukwu and the Okpankpo council of household heads. Their military arm was outsourced — the Abam, Ohafia and Edda warriors of the Cross River area, recipients of yam tribute from the Aro, supplied raiders for slave campaigns. The Aro also dispersed permanent trading settlements (the Aro diaspora) deep into Igboland and beyond, where they retained Aro identity and gave the patronymic 'Aro' to their children: this Aro diaspora is the origin of the famous Aro merchant houses of Aba, Onitsha, Enugu, Calabar, and even Lagos.
The trans-Atlantic abolition (1807 British, 1834 US, 1888 Brazilian) gradually closed the export market, but the Aro converted the slave trade into a domestic palm-oil and provisioning trade with the Niger Coast Protectorate. The Aro were also the largest interior cowrie-credit clearinghouse in the Bight of Biafra: prices across hundreds of inland markets were quoted in cowries cleared through Aro factor-houses. When the British flooded Lagos with Zanzibar ring cowries from the 1840s and crashed the shell's purchasing power by over 80% between 1851 and 1869 (see How the currency fell before the flag), the Aro credit network — denominated in a currency the British were destroying — was already structurally bankrupt before the soldiers arrived. The British, frustrated by Aro obstruction of direct trade with the Igbo hinterland, launched the Anglo-Aro War of 1 December 1901 to 24 March 1902. Colonel Arthur Festing's 1,500-man force advanced from four directions; the Long Juju at Arochukwu was destroyed with dynamite on 28 December 1901; the Aro priests were executed or scattered.
The Anglo-Aro War opened Igboland to direct British administration and created the colonial framework that produced the Warrant Chiefs system — the system that, twenty-seven years later, would provoke the 1929 Aba Women's War. The Eze Aro stool was restored in the colonial period and continues; the Ibini Ukpabi grove at Arochukwu is today a heritage tourism site.