How did the Mongols build the largest contiguous land empire?

The Mongols combined political unification under Chinggis (Genghis) Khan, a highly organized and mobile cavalry army, and a willingness to use terror against those who resisted. By his death in 1227 the empire stretched from northern China to Central Asia and the edges of Eastern Europe. His successors then added administration, taxation and communication networks to hold the conquests together. Scholars do not agree on a single reason why the Mongols burst out of Mongolia. [1] [2]

In 1206 Temujin called a kurultai, an assembly of loyal followers, to confirm his rule over all Mongols. According to the Secret History of the Mongols, nearly all of the roughly million people attended, and a shaman proclaimed him Chinggis Khan with the backing of the god Tengri. He decreed that future great khans be chosen by a kurultai rather than by family succession alone, and he issued rules called the yassa, later written down in a script based on Uyghur writing. [3]

Peace had a cost. The new order banned raiding between clans, which had been a path to wealth and status. OpenStax argues that Chinggis saw conquest of settled peoples as the way to supply new wealth and glory. [3]

The army was made up of light and heavy cavalry organized on a decimal system: squads of ten, troops of 100, regiments of 1,000 and a tuman of 10,000. Three tumans normally formed an army. WarHistory.org credits this flexibility, along with strategic mobility and the quality of warriors and horses, for the Mongols' success. A book on the Mongol military system likewise attributes their dominance to organization and to tacticians such as Subutai carrying out practiced maneuvers, not to unchecked ferocity. [4] [5]

The Kara-Khitan and Xi Xia accepted tribute status, but the Jin did not. In 1210 Chinggis invaded the Jin with a smaller army, presented himself to the resentful Khitan as a liberator, and gained defectors before taking and looting the capital Zhongdu. The wealth gained pushed the Mongols to look west. Around 1218 a Khwarazmian governor killed a Mongol trade caravan, and the Khwarazmian ruler killed most of the envoys sent to demand compensation. The Mongols responded with a war of revenge that devastated cities such as Herat, Merv and Nishapur. By 1223 the Khwarazmian ruler was dead and his realm was divided among Chinggis's sons and generals. [3]