Complex sentence: After the emperor's second excommunication, Benno tried to bring about a reconciliation, but, seeing the insincerity of the emperor, gave up in despair and retired to the monastery of Iburg, which he had founded in 1070.
Split into simpler sentences: After the emperor's second excommunication, Benno tried to bring about a reconciliation. He retired to the monastery of Iburg, which he had founded in 1070.