This book seems to be one after Li Shuo's previous book on history of war equipment: South-North period. Li Shuo's book is a must read.
In the first book, one place is most striking. Li Shuo visited Nanjing and walked on the old city wall. There he looked north on the Yangtze river. At this particular moment, the author thought about Liu Jinu and his successful campaign to recover the lands of North Yangtze River. Same place, yet thousand years apart! Well, well, that is when history becomes suddenly relevant to our current life.