Complex sentence: He only retained power in Italy as long as he was personally there, he was vigorously opposed by Lambert's mother, Agiltrude, and when he left, having taken ill, most of Italy was in Lambert's supporters' hands.
Split into simpler sentences: He only retained power in Italy as long as he was personally there. He was vigorously opposed by Lambert's mother, Agiltrude, and when he left, having taken ill, most of Italy was in Lambert's supporters' hands.