Complex sentence: However Rome had allready begun the conversion of Anglo-Saxons from the south with a mission to Kent in 577, and differing with Rome on the date to celebrate Easter, the Irish mission withdrew from Lindisfarne back to Iona.
Split into simpler sentences: However Rome had allready begun the conversion of Anglo-Saxons from the south with a mission to Kent in 577. There arose a conflict between the Irish monks and Rome on the date to celebrate Easter, so the Irish mission withdrew from Lindisfarne back to Iona.