Complex sentence: However, on his reappearance after a traumatic journey through the Zambezi valley, Mzilikazi asserted control and had his son and all those chiefs who had chosen him put to death.
Split into simpler sentences: However, on his reappearance after a traumatic journey through the Zambezi valley, Mzilikazi asserted control once more. According to one account he had his son and all those chiefs who had chosen him put to death.