The crusade had also been marked by a significant escalation in longstanding tensions between the feudal states of western Europe and the Byzantine Empire. During the crusade, Frederick I, Holy Roman Emperor, had almost besieged Constantinople because of the failure of the Byzantines to provide him with safe passage across the Dardanelles. The Byzantines for their part suspected him of conspiring with the breakaway Byzantine provinces of Serbia and Bulgaria. King Richard I of England also seized the breakaway Byzantine province of Cyprus. Rather than return it to the Empire, he sold the island to the Knights Templar.