Complex sentence: On the death of his great-nephew Theodebald in 555, Clotaire annexed his territories; and on Childebert's death in 558 he became sole king of the Franks.
Split into simpler sentences: On the death of his great-nephew Theodebald in 555, Clotaire annexed his territories. On Childebert's death in 558 he became sole king of the Franks.