Complex sentence: Queen Mbaao was left with the responsibility to migrate the Mbunda to better settlement lands from Kwilu/Kasai, and they embarked on their second migration expedition to the southeast of Kwilu and Kasai rivers.
Split into simpler sentences: Queen Mbaao was left with the responsibility to migrate the Mbunda to better settlement lands from Kwilu/Kasai. During Queen Mbaao's reign, Mbundas embarked on their second migration expedition to the southeast of Kwilu and Kasai rivers.