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Resumption of hostilities: 1394–1424

In 1394, relations between the Byzantines and the Ottomans changed for the worse and the war between the two resumed when the Ottoman Sultan Bayezid (ruled 1389–1402) ordered the execution of Manuel II, after the Emperor attempted to reconcile with his nephew John VII. The Ottoman Sultan then later changed his decision and demanded that a mosque and a Turkish colony be established in Constantinople. Manuel II not only refused this, he also refused to pay the Sultan tribute and went so far as to ignore the Sultan's messages, leading to a siege of the city in 1394. Manuel II called for a Crusade, which came in 1396. Under the future Holy Roman Emperor Sigismund, the Crusade was routed at Nicopolis in 1396.

The defeat convinced Manuel II to escape the city and travel to Western Europe for aid. During this time the reconciled John VII led the city's successful defense against the Ottomans. The siege was finally broken when Timur of the Chagatai Mongols led an army into Anatolia, dismantling the network of beyliks loyal to the Ottoman Sultan. At the Battle of Ankara, Timur's forces routed Bayezid I's forces, a shocking defeat for which no one was prepared. In the aftermath, the Ottoman Turks began fighting each other led by Bayezid's sons.

The Byzantines wasted no time exploiting the situation and signed a peace treaty with their Christian neighbours and with one of Bayezid's sons. By signing the treaty, they were able to recover Thessalonika and much of the Peloponnese. The Ottoman civil war ended in 1413 when Mehmed I, with the support of the Byzantine Empire, defeated his opponents.

The rare amity established between the two states would not last; the death of Mehmed I and the rise of Murad II in 1421 coupled with the ascent of John VIII to the Byzantine throne led to a deteriorated change in relations between the two. Neither leader was content with the status quo. John VIII made the first and foolish move by inciting a rebellion in the Ottoman Empire: a certain Mustafa had been released by the Byzantines and claimed that he was Bayezid's lost son.

Despite the odds, a sizable force had mustered in Europe under his banner, defeating Murad II's subordinates. Murad II's furious reply eventually smashed this upstart and, in 1422, began the Siege of Thessalonika and Constantinople. John VIII then turned to his aging father, Manuel II, for advice. The result was that he incited yet another rebellion in the Ottoman ranks — this time supporting Murad II brother's claim, Kucuk Mustafa. The seemingly promising rebellion had its origins in Asia Minor with Bursa coming under siege. After a failed assault on Constantinople, Murad II was forced to turn back his army and defeat Kucuk. With these defeats, the Byzantines were forced once more into vassalage – 300,000 coins of silver were to be delivered to the Sultan as tribute on an annual basis.