As we have seen, a strong vein of mutual toleration characterised relations between the Byzantine and the Turkish ruling families in the twelfth and thirteenth centuries. Individual careerists and exiles moved between their respective courts in quest of advancement or asylum, and the Seljuq sultan generally showed little inclination to try and take full advantage of those occasions when the Byzantine administration in western AsiaMinor was in disarray. It was, above all, the coming of theMongols – their erosion of the power of the Rum sultanate to the advantage of individual warlords and their savage measures against local populations in eastern AsiaMinor – that prompted the migration of sizable numbers of Turks westwards, swamping the Byzantine defences. Andronikos II’s administrative deficiencies and general disregard for Asia Minor further aggravated the situation. But, as so often in Byzantine history, the mainsprings of action lay far beyond the empire’s borders or means of control. The Turkish conquest of 1302–5 was more than a simple nomadic invasion, seeing that sedentary and transhumant elements had long co-existed in the border zone. After the Turks’ conquest of what was left of Byzantine Asia Minor, not only did nomads settle in their newly conquered lands, but these lands also soon became the target of Muslim immigration from the depths of central and eastern Asia Minor, leaving the dwindling Greek communities little chance of survival. This rapid change in the ethnic balance meant there was no hope of Byzantium recovering its lost provinces in western Asia Minor. When the Catalans finally departed, they left an empire that was devastated and bankrupt. Byzantium’s former possessions in western Anatolia were divided between various Turkish warlords, who managed to establish successful principalities along the coasts of the Aegean and the Sea of Marmara. One such Bithynian beylik – that of Osman – would become the cradle of a new formation: the Ottoman Turks.