Genghis Khan was one of the most famous conquerors in world history, building the foundations of what became the largest land empire ever created (only the British Empire was larger). His general Sübe'etei was probably his best commander, and helped Genghis and his immediate successors expand the Empire, leading campaigns in China, around the Caspian Sea and even reaching Western Europe. Despite their fame, the exact details of their military campaigns aren't terribly well understood, with many of their exploits exaggerated by their opponents.
The author uses a wider range of sources than most English language works on the Mongols, including some surprisingly (and frustratingly) un-translated Chinese dynastic histories. This helps provide a balance for the famous Secret History of the Mongols, and helps pick up its (generally fairly minor) errors. It also allows him to follow some of the better documented campaigns in great detail - almost day-by-day on occasions.
The text can be a bit hard to follow on occasions, mainly because of the large number of people involved and the frequent changes of sides. This gets worse after the Mongols gained many Chinese followers and commanders, and we end up with clashes between Chinese generals in the service of one of the Chinese dynasties and Chinese generals in the service of the Mongols.
The text is supported by a large number of comparatively small scale maps, which help us follow the individual campaigns, but I would have liked at least one large scale map showing the situation at the start of Genghis's career, and in particular the locations of the main dynasties he faced. I'm not always 100% convinced by the author's approach to troop numbers, which is generally to massively reduce the amount of troops opposed to the Mongols, often bringing them to parity with their opponents.
The detailed narratives make you realise just how impressive some of the Mongol's achievements actually were. Genghis Khan's most impressive moments probably come during the establishment of his power in Mongolia, where he had to overcome more numerous opponents who fought in the same way as his men. Sübe'etei comes across as the more impressive of the two - in particular his circumnavigation of the Caspian Sea, where he led a fairly small Mongol army through a whole series of hostile states (admittedly mainly hostile because a Mongol army was invading), and his campaign in Europe, where he was able to defeat a series of European armies while operating thousands of miles away from his homeland.
Not all of the Mongol conquests emerge quite as impressively. Genghis Khan's famous invasion of Khwarezm appears in a different light - an attack on a fairly weak opponent, which had only recently established control of the areas first invaded. Likewise in China the Mongols were lucky not to face a strong united opponent - instead China was split between the Xia, Jin and Song, and these states fought each other and even supported the Mongols against each other, greatly aiding the Mongol conquest.
This is a very valuable addition to the literature on the Mongol conquests, giving us a much clearer idea of the detailed course of their campaigns, the world in which they took place, and the methods used to win them.
Part I: Genghis Khan
Part II: Sübe'etei
Author: Carl Fredrik Sverdrup