Ottoman Interregnum: Süleyman Çelebi defeats his brother Musa Çelebi outside the Byzantine capital, Constantinople.

The Ottoman Interregnum, or Ottoman Civil War, was a civil war in the Ottoman realm between the sons of the Ottoman sultan Bayezid I following their father's defeat and capture by Timur in the Battle of Ankara on 28 July 1402. Although Timur confirmed Mehmed Çelebi as sultan, Mehmed's brothers refused to recognize his authority, each claiming the throne for himself, which resulted in civil war. The Interregnum would last a little under 11 years and culminate in the Battle of Çamurlu on 5 July 1413, when Mehmed Çelebi emerged as victor, crowned himself Sultan Mehmed I, and restored the empire.

Süleyman Çelebi was an Ottoman prince and a co-ruler of the Ottoman Empire for several years during the Ottoman Interregnum. There is a tradition of Western origin, according to which Suleiman the Magnificent was "Suleiman II", but that tradition has been based on an erroneous assumption that Süleyman Çelebi was to be recognised as a legitimate sultan.

The Battle of Kosmidion occurred on 15 June 1410, during the Ottoman Interregnum, and was fought between the forces of the rival brothers, Musa Çelebi and Süleyman Çelebi, at Kosmidion just outside the land walls of Constantinople.

Musa Çelebi was an Ottoman prince and a co-ruler of the empire for three years during the Ottoman Interregnum.

Constantinople was a historical city located on the Bosporus that served as the capital of the Roman, Byzantine, Latin and Ottoman empires between its consecration in 330 and 1930, when it was renamed Istanbul. Initially as New Rome, Constantinople was founded in 324 during the reign of Constantine the Great on the site of the existing settlement of Byzantium and in 330 became the capital of the Roman Empire. Following the collapse of the Western Roman Empire in the late 5th century, Constantinople remained the capital of the Eastern Roman Empire, the Latin Empire (1204–1261) and the Ottoman Empire (1453–1922). Following the Turkish War of Independence, the Turkish capital moved to Ankara. Although the city had been known as Istanbul since 1453, it was officially renamed Istanbul on 28 March 1930. The city is today the largest city in Europe, straddling the Bosporus strait and lying in both Europe and Asia, and the financial center of Turkey.