Complex sentence: Irish missionaries led by Saint Columba based in Iona (from 563) and elsewhere converted many Picts and the court of Anglo-Saxon Northumbria, and the Gregorian mission, who landed in 596, did the same to the Kingdom of Kent.
Split into simpler sentences: Irish missionaries led by Saint Columba based in Iona (from 563) and elsewhere, converted many Picts. The court of Anglo-Saxon Northumbria, and the Gregorian mission, who landed in 596, did the same to the Kingdom of Kent.