A distinguishing feature of Constantinople in its role as the capital of the Byzantine Empire was that it often became the scene of struggles for the imperial throne. Since the civil war of 1341–7 between John VI Kantakouzenos and the partisans of John V Palaiologos, it had become almost customary for claimants to the Byzantine throne to run to the Turks for assistance. But what course was a claimant to follow when the ruling emperor himself happened to be officially allied with the Ottomans? In 1373 while Emperor John V was serving on an Ottoman campaign in Asia Minor in compliance with his recent agreement with Murad I whereby he had become a tributary vassal of the Ottomans, his son and regent, Andronikos IV, and the Sultan's son Savcı Çelebi prepared a joint plot to overthrow their fathers. John V and Murad I responded to this conspiracy by likewise joining forces against their sons. Within a few months the movement was suppressed, and the young princes were captured. After having Savcı blinded and beheaded, Murad I ordered the Emperor to put out the eyes of his own son. John V reluctantly obeyed, but made sure that Andronikos did not lose his sight completely. For the time being, the failed usurpation additionally cost Andronikos his right of succession to the Byzantine throne, which was transferred to his younger brother Manuel (II).