he peaceful period Byzantium had enjoyed during the reign of Mehmed I ended when he died. His son and successor, Murad II, carried on the aggressive policies of Bayezid. The fact, moreover, that the son of Manuel II, John, who had been crowned co-Emperor in January 1421, had endeavoured to support Mustafa, his rival, had infuriated Murad II. After he had dealt with Mustafa, he sent an army to blockade Thessalonike, while he himself conducted a short siege of Constantinople (June-September 1422).

The siege of the Byzantine capital was not successful, as Murad II had to confront a new rival to his throne at Prousa. Although he gave up the siege of the capital, Murad II continued to besiege Thessalonike, while, in the spring of 1423, Turkish troops invaded Albania and the Peloponnese, wreraking terrible havoc. In Thessalonike, the siege forced the governor of the city, Andronikos Palaiologos, to surrender it to the Venetians in the summer of 1423, to prevent it from falling into Turkish hands. The Venetians promised to respect the rights of the citizens and undertook to ensure the defence and provisioning of the city.

The situation was once again becoming dangerous for the Empire, forcing the co-Emperor, John, to appeal to the West for aid. However, the negotiations with the Venetians and the Hungarians (1423-24) did not result in any effective offer of support. Having returned to Constantinople empty-handed, John initiated negotiations with the Turks, which led, in February 1424, to a new agreement, the terms of which were very harsh for the Byzantines. For the second and last time they were forced to pay tribute to the Turkish Sultan. Manuel II, whose health was failing after the continuous frustration of his efforts, abdicated in 1425. He was succeeded by John VIII, who now officially ascended the throne and assumed the powers he had in effect exercised since the day he had been made co-Emperor. The aged emperor died as monk Matthew on 21 July 1425.