‘Strangely enough’, avows Peter Jackson, ‘a knowledge of Mongolian did not prove necessary for writing this book.’ He is, however, at home with Mongolian and many other relevant languages (including Arabic) and profound scholarship is used to produce an authoritative, comprehensive synthesis of the Mongols' relations with Latin Christendom, the first to appear in English, and the best in any language. Jackson's mastery of the source materials enables him to place the subject in proper perspective. He points out that the subjugation and exploitation of China (p. 4) was of overriding interest to the Mongols. One of his underlying themes is that the Mongols were of markedly greater interest to Latin Christendom than vice-versa, and this bedevils attempts to discern Mongol attitudes through the filter of non-Mongol sources. The author none the less expounds the thought-world of the Mongols, the priorities of those living as nomads and the many facets of Mongol political culture once numerous recruits from sedentary societies were in the khan's employ. The opening chapters set the scene on the eve of the Mongols' first strike against Latin Europe: Latin Christendom itself, still expansionist, optimistic yet riven by bitter disputes; and Inner Asia, where Chinggis Khan brought his people and newly-subjugated neighbours an ethos of victory, while paying keen attention to the susceptibilities, religious and otherwise, of those not yet conquered. Subsequent chapters recount the invasions of the Hungarian, Polish and Dalmatian lands in the early 1240s; Innocent iv's vigorous diplomatic response, despatching ambassadors to Mongol power centres and attempting to create a bloc of buffer states between the core-lands of Christendom and the Mongols, while also contemplating a crusade against them; the Mongol conquests in the Middle East and the halting of their invasions into eastern Europe after 1259 due to internal dynastic strife; the intensive exchanges of western popes and potentates with the Mongol rulers of Persia; the development of a modus vivendi between the Golden Horde and Eastern Europe, despite periodic flurries of belligerence, and the Mongols' transformation into the role of potential allies of weak eastern European rulers or their rivals in their internecine conflicts. One chapter is devoted to the dealings of the western powers and Byzantium with a new Mongol warlord Temür (Tamerlane): the hopes of an alliance with him against the Ottoman sultan that Archbishop John of Sultaniyya fanned are coolly appraised and found wanting.

These essentially narrative chapters are interwoven with thematic chapters devoted to the diverse images of Mongols circulating among westerners; religious missions to the khans; trading conditions in the lands under Mongol rule and the commercial opportunities which westerners, especially the Genoese seized; and the quality and quantity of fresh data about the east that became available to westerners through travellers returning thence: in Jackson's words, texts of travel literature ‘took on a life of their own’. These chapters teem with ideas and insights and are a methodological model for all students of medieval Christendom's relations with external cultures and peoples.

The optimism voiced by some churchmen that the Mongols might be converted to Christianity is scrutinised, and the quotient of wishful thinking assessed. Those agents of Christendom who observed the Mongols at firsthand were more hard-headed, and astute. Thus William of Rubruk commented on the ambivalence of Khan Möngke towards proponents of major religions: ‘He believes in none of them … and yet they all follow his court as flies do honey.’ The friar-emissaries' powers of observation and rational analysis are discussed by Jackson, and he evaluates the extent of apocalyptic thought in their writings: explicit references to the peoples of the apocalypse by friars who went east between 1245 and 1255 are few. The wealth of detail and – where at all verifiable – accuracy of these friars' empirical observations might perhaps have been brought out more heavily. After all, Rubruk and John of Plano Carpini rank as prime sources for the ethnography, topography, flora and fauna of the Crimea and the Black Sea steppes in the Middle Ages. Their blend of intensive faith, curiosity and intellectual rigour has no known medieval precedents.