Complex sentence: After this date the events at Amarna and their chronology become far less clear and it is only with the accession of Tutankhamun and the restoration early in this king's reign that matters become clearer again.
Split into simpler sentences: After this date the events at Amarna and their chronology become far less clear. It is only with the accession of Tutankhamun, and the restoration early in this king's reign, that matters become clearer again.