Complex sentence: The relations between the Muslims and their pagan fellow-tribesmen rapidly deteriorated; while the Quraysh had not previously shown significant opposition to Muhammad and his followers, his denunciation of the Meccan idols provoked hostile reactions.
Split into simpler sentences: The relations between the Muslims and their pagan fellow-tribesmen rapidly deteriorated. While the Quraysh had not previously shown significant opposition to Muhammad and his followers, his denunciation of the Meccan idols provoked hostile reactions.