part from the developments in the Balkans, where the Serbs were spreading over Byzantine territories in Macedonia, another factor which determined the foreign policy of Andronikos III was the continuous advance of the Turks in Asia Minor. In spite of the state's weakness, mainly due to the recent civil war, the Emperor, along with his collaborator and megas domestikos, John Kantakouzenos, took immediate action in the region.

In 1329 they attacked the Ottomans, who were besieging Nicaea. However, they were defeated at the battle of Philocrene in March 1331, and the city which, two generations before, had been the centre of the Empire, was now lost. A few years later (1337), Nikomedeia also fell into the hands of the Ottomans. Now, only a few cities such as Philadelphia and Herakleia Pontike continued to belong to Byzantium.

In their fight against the Ottomans and Latins in Asia Minor and the islands of the northern Aegean, the Byzantines had the support of the Seljuk Turks, since both were threatened by the same enemies. It was, besides, with the assistance of the Seljuks that the Byzantines had been able to restore their rule in the north-eastern Aegean, at the expense of the Genoese, by conquering Phokaia and Lesbos (1335-6).

Despite the efforts of the Byzantines, who, according to circumstances, sought help against the Ottomans either from the West and the Pope, or from the Seljuks of the East, the Ottomans continued to extend their sway, and having occupied the coast of Bithynia, they embarked on naval operations directed towards the European shores of Byzantium.