From July 20, 1402, until July 5, 1413, the Ottoman Interregnum, often known as the Ottoman Civil War, lasted. It was fought between Sultan Bayezid I's sons following their father's defeat in the Battle of Ankara on July 20, 1402. Despite Timur's confirmation of Mehmed Çelebi as sultan, his brother’s İsa Çelebi, Musa Çelebi, Süleyman Çelebi, and eventually Mustafa Çelebi refused to acknowledge his authority, demanding the throne for themselves. The result was the civil war. The Interregnum lasted just over 11 years, until Mehmed Çelebi triumphed in the Battle of Amurlu on July 5 1413, crowned himself Sultan Mehmed I, and restored the empire.
İsa and Mehmed
Following Sultan Bayezid I's death in 1403, a civil war broke out among his sons. Süleyman, his oldest son, governed the newly acquired Bulgaria, all of Thrace, Macedonia, and northern Greece from Edirne. İsa Çelebi, the second son, established himself as an independent monarch in Bursa, while Mehmed built a kingdom in Amasya. Mehmed and İsa went to war, and after the battles of Ermeni-beli and Ulubad (March-May 1403), İsa retreated to Constantinople, while Mehmed captured Bursa. The succeeding combat between Mehmed and Isa at Karasi ended in Mehmed's triumph, with İsa retreating to Karaman. Mehmed's agents eventually assassinated İsa in a bath.
Süleyman Enters Civil War
Meanwhile, Timur released Musa Çelebi, Bayezid's other surviving son, who had been captured in the Battle of Ankara, into the care of Yakub of Germiyan. After Mehmed submitted a request for his brother's release, Mûsa was set free. Süleyman crossed the straits with a massive force after Isa's death. Süleyman was first successful. He invaded Anatolia in March 1404, taking Bursa and Ankara later that year. Mehmed dispatched Musa over the Black Sea to Thrace with a small force to attack Suleyman's possessions in south-eastern Europe during the stalemate in Anatolia, which lasted from 1405 until 1410. Suleyman was summoned to Thrace as a result of this action, and a brief but bloody battle ensued between him and Mûsa. Suleyman had the upper hand initially, winning the battle of Kosmidion in 1410, but his army deserted to Mûsa at Edirne in 1411, and Suleyman was beheaded on Musa's orders. After that, Mûsa was the Ottoman ruler of Thrace's Ottoman dominions.
Mehmed and Musa
The Byzantine emperor Manuel II Palaiologos had been Suleyman's ally, so Mûsa besieged Constantinople. Manuel requested Mehmed's protection, and Mehmed's Ottomans defended Constantinople against Musa's Ottomans of Thrace. Mehmed launched many fruitless attacks against his brother's forces and was forced to recross the Bosporus to put down a rebellion that had erupted in his lands. Mûsa was now intensifying his siege of Constantinople. Mehmed returned to Thrace and enlisted the help of Serbian Despot Stefan Lazarevic. On the plain of Chamurli, the armies of the rival Ottoman brothers clashed (today Samokov, Bulgaria). Hassan, the Janissaries of Mehmed's Agha, walked out in front of the columns and attempted to persuade the warriors to switch sides. Mûsa went towards Hassan and killed him, but an officer who had followed Hassan wounded him. Mûsa's Ottomans fought bravely, but Mehmed and his allies won the battle. Mûsa escaped and was eventually apprehended and strangled. With Mûsa's death, Mehmed became Sultan Mehmed I, the late Sultan Bayezid I's only surviving son. The Interregnum exemplified the fratricide that would become all too typical in Ottoman successions.
Only Mehmed minted coins with the title Sultan during the Interregnum. Suleyman's coinage identified him as Emir Suleyman b. Bayezid, whereas Musa's coins identified him as Musa b. Bayezid. Isa's coins have never been found.