Denis Crispin Twitchett was a British Sinologist and scholar who specialized in Chinese history and greatly expanded the role of Chinese studies in Western intellectual circles.
In a certain way, politically the Song dynasty after Tang was an aftermath of the state development in the steppe area. Due to the incompatibility between power centralization and military necessity to maintain a forth at the border that is powerful enough to topple the court, Tang led a downward path ever since the An Lu Shan rebellion. The agricultural civilization at the south of the steppe never worked out a solution to the situation. In this sense, I decided to move on to the part 2 of Song Cambridge history, and focus its intellectual development, where a Zhu Xi re-invented Confucianism. Only the first introduction chapter was read.