Isa and Mehmed
Civil war broke out among the sons of Sultan Bayezid I upon his death in 1403. His oldest son, Suleyman, with his capital at Adrianople, ruled northern Greece, Bulgaria and Thrace. The second son, İsa Çelebi, established himself as an independent ruler at Bursa and Mehmed formed a kingdom at Amasya. War broke out between Mehmed and İsa, and following the battles of Ermeni-beli and Ulubad(March-May 1403), Isa fled to Constantinople and Mehmed occupied Bursa. The subsequent battle at Karasi between Mehmed and Isa resulted in a victory for Mehmed and Isa fleeing to Karaman. Isa was later killed in a bath by agents of Mehmed.
Read more about this topic: Ottoman Interregnum