Complex sentence: His efforts to secure an effective authority over his Irish lands were only moderately successful; and after holding a parliament at Kilkenny, which passed the celebrated Statute of Kilkenny in 1366, he dropped the task in disgust and returned to England.
Split into simpler sentences: His efforts to secure an effective authority over his Irish lands were only moderately successful. After holding a parliament at Kilkenny, which passed the celebrated Statute of Kilkenny in 1366, he dropped the task in disgust and returned to England.