Complex sentence: After the army's recovery Hannibal offered them peace by formal alliance and when it was refused surrounded their chief settlement, leveled it and executed all his opponents as an object lesson to the other tribes in the north.
Split into simpler sentences: After the army's recovery, Hannibal offered them peace by formal alliance. When it was refused, he surrounded their chief settlement, levelled it and executed all his opponents as an object lesson to the other tribes in the north.