This was my favorite division of the three books I've read covering parts of Sima Qian. I particularly enjoyed the chapters covering the Xiongnu and other "barbarian" people including the Yue, Yuezhi, and Ferghana. It is clear from these chapters that the Xiongnu were formidable opponents that the Han were often forced to treat as equals in both times of peace and war. It was exciting to learn more about the dynamics of the Xiongnu and of the military and political leaders involved in the conflicts, as well as the dynamics surrounding revolts among the Yue. The chapters covered here, more than what I've previously read from Sima Qian, really show how Han China was enmeshed in a wider geopolitical setting - and that the dynasty's fate was very much intertwined with the ongoings of peoples outside of, as well as along the margins of, the empire.
Highly recommended reading for anyone with an interest in ancient China. If you have to read just one volume excerpting Sima Qian, read this one.