Concept:The Shehus strengthened their authority in Borno by reorganising the military under their direct control.Explanation:Before the Shehus, military power was largely held by regional chiefs and nobles.This made it difficult for the central ruler to maintain full authority.The Shehus introduced a system where the military was centralised and brought directly under the state administration.This change helped them reduce the influence of powerful nobles and secure their hold over Borno.It also improved the effectiveness of the state in defending against external threats.Answer:Centralisation of the military.