Complex sentence: In order to accomplish the task, he secluded himself for two years; and, on the cause of his retirement becoming known to the emperor Alexander, Karamzin was invited to Tver, where he read to the emperor the first eight volumes of his history.
Split into simpler sentences: In order to accomplish the task, he secluded himself for two years. When emperor Alexander learned the cause of his retirement, Karamzin was invited to Tver, where he read to the emperor the first eight volumes of his history.