When Andronikos III died in 1341, his underage son John V Palaiologos inherited the throne. Disputes between John V's mother Anna of Savoy and the Patriarch John XIV on one side and Andronikos III's friend and "megas domestikos" John Kantakouzenos on the other led to a new and devastating civil war, lasting until 1347 and won by John Kantakouzenos, who became senior co-emperor as John VI. The weakening of Byzantium as a result of the civil war allowed Stefan Dušan of Serbia to invade Macedonia, Thessaly and Epirus in 1346–1348, creating the Serbian Empire. In the meantime, John VI Kantakouzenos attempted to consolidate his own dynasty on the imperial throne, marrying his daughter Helena to John V and proclaiming his son Matthew Kantakouzenos as co-emperor. Clearly intending to usurp the throne, a new series of civil wars from 1352 to 1357 were eventually won by John V, deposing the Kantakouzenoi. In 1382, the Kantakouzenoi were also driven out of the Morea (the modern-day Peloponnese) and John V's son Theodore was placed to govern it as the semi-independent Despot of the Morea, an important victory as the region was quickly becoming the most important Byzantine province. The Byzantine civil wars, and the collapse of Stefan Dušan's Serbian Empire following his death in 1355, had allowed the Ottoman Turks to expand almost unopposed through the Balkans and in the second half of the 14th century, the empire passed almost without a fight under Ottoman sovereignty, forced to pay tribute and offer military aid if needed.