Complex sentence: They considered the pilgrimage to Mecca a superstition and once in control of the Bahraini state they launched raids along the pilgrim routes crossing the Arabian Peninsula: in 906 they ambushed the pilgrim caravan returning from Mecca and massacred 20,000 pilgrims.
Split into simpler sentences: They considered the pilgrimage to Mecca a superstition and once in control of the Bahraini state they launched raids along the pilgrim routes crossing the Arabian Peninsula. In 906 they ambushed the pilgrim caravan returning from Mecca and massacred 20,000 pilgrims.