Complex sentence: He remained in charge of the city until 1418, when he attempted to suppress a rebellion to the south of Smyrna headed by Sheikh Bedrettin's follower Börklüce Mustafa.
Split into simpler sentences: He remained in charge of the city until 1418. In that year, he attempted to suppress a rebellion to the south of Smyrna headed by Sheikh Bedrettin's follower Börklüce Mustafa.