Episode 1.5 is about Yang Jian, Emperor Wen of Sui, or, Sui Wen-di. Emperor Wen unified China for the first time in 300 years, since the great Han Dynasty. In doing so, he helped to usher in 6 centuries of unified and ascendant China.
The Cambridge History of China, Ed. Denis C. Twitchett
Ann Paludan, Chronicle of Chinese Emperors
Victor Cunrui Xiong, Historical Dictionary of Medieval China
Charles Holcombe, Southern Integration: The Sui-Tang (581-907) Reach South
Denis A Graff, Medieval Chinese Warfare, 300-900 AD