The Genoese held the colony of Galata, a suburb of Constantinople across the Golden Horn, as part of the Treaty of Nymphaeum of 1261. This agreement established trade relations between the two powers and granted Genoa extensive privileges within the empire, including the right to collect customs dues at Galata. The Byzantine Empire was still reeling from the civil war of 1341–1347, and these concessions made a recovery difficult. Constantinople collected only thirteen percent of all custom dues from shipping passing through the Bosphorus, only 30,000 hyperpyra a year, with the rest going to Genoa.

The Byzantine–Genoese War of 1348–1349 was fought over control over custom dues through the Bosphorus. The Byzantines attempted to break their dependence for food and maritime commerce on the Genoese merchants of Galata, and also to rebuild their own naval power. Their newly constructed navy however was captured by the Genoese, and a peace agreement was concluded.

The failure of the Byzantines to expel the Genoese from Galata meant that they could never restore their sea power, and would thenceforth be dependent either on Genoa or Venice for naval aid. From 1350, the Byzantines allied themselves to the Republic of Venice, which was also at war with Genoa. However, as Galata remained defiant, the Byzantines were forced to settle the conflict in a compromise peace in May 1352.