Complex sentence: The Duke of Guise and his relations, Mayenne, Aumale, Elboef, Mercoeur and the Duke of Lorraine controlled extensive territory that was controlled by the League which also had a following among the urban middle classes.
Split into simpler sentences: The Duke of Guise and his relations, Mayenne, Aumale, Elboef, Mercoeur and the Duke of Lorraine controlled extensive territories that were loyal to the League. The League also had a following among the urban middle classes.