Which dynasty is the story of Lonely World?

This TV series tells the story of the Northern Wei Dynasty, the Northern Zhou Dynasty and the Sui Dynasty.

Based on the turmoil in the ruling and opposition parties at the end of the ancient Northern Zhou Dynasty, the play tells the story that the three daughters of Du, Prajna, Galo, who are important ministers, gradually changed from noble families to royal daughters because of the divination of "being alone in the world".

(Quoted from Baidu Encyclopedia Dugu Tianxia Entry)