Ottoman Beylik Expansion (1340s)

Timeline

1. 1341–1343Thrace frontier · ThraceAfter the Byzantine civil war broke out, Cantacuzenus sought Orhan's aid. Around 1343 Ottoman cavalry entered Thrace in large numbers for the first time, assisting Cantacuzenus against the regency faction and the Serbian alliance. In return, the Ottomans gained privileges to garrison and levy taxes within Byzantine territory, and tightened pressure on Byzantine remnants in Bithynia.
2. 1344–1345Bithynia · BithyniaIn 1345 Cantacuzenus's daughter Theodora married Orhan, marking a shift from mere mercenary ties to dynastic bonds. Meanwhile the Ottomans continued to nibble away at Byzantine fortresses in Bithynia and along the Sea of Marmara, including the area around Nicomedia (İzmit), laying the groundwork for further overseas expansion in the 1350s.
3. 1346–1350Gallipoli Peninsula · ThraceAfter Ottoman reinforcements helped Cantacuzenus prevail in 1346–1347, the Ottomans obtained long-term garrison rights in Thrace. By the late 1340s Ottoman power approached the Dardanelles, and in Anatolia established control over the Bursa–Eskişehir axis. Before Orhan's death in 1359, the Ottomans had grown from a frontier beylik into a core threat to Byzantine survival.