Emperor John VIII Palaiologos encourages a Turkish pretender at the death of Ottoman sultan Mehmed I in 1421 in hopes of preventing the ascent of eighteen-year-old Murad II and thereby causing disruption within the ranks and leadership of the Ottoman Empire.

Murad crushes the plot, then revokes all the privileges that the Turks had granted the Greeks after lifting their siege of Constantinople in 1399.

The Ottomans besiege Constantinople again in 1422, but the combination of stiff resistance by the defenders and the city’s nearly impregnable walls force the attackers to retire. (Another factor prompting the Turkish withdrawal may have been Murad’s necessary return to the Ottoman capital to prevent another pretender, also possibly encouraged by Constantinople, from usurping power.)

Murad, called the Restorer, has by 1430 reestablished Ottoman control of Thessaly and Macedonia, occupied Anatolia's Aegean coast, and won Salonika in a war with Venice.