How did Usman dan Fodio establish the Sokoto Caliphate? The declaration of the holy war spread across the Hausaland and many people volunteered to join his army. In 1804, he formally declared a holy war on the whole of Hausaland. In 1808, Usman and his followers conquered Gobir, Kano, and other Hausa city-states. He retired from battle in 1811 and returned to teaching and writing but his armies continued their conquests until 1815. A religious teacher who became the leader of a revolution: Usman dan Fodio, respectfully referred to as Sheikh,...