Their light cavalry was also fairly effective in forested places like Hungary or Manchuria.  Genghis was far from the best Mongol general but he personally achieved some impressive victories by attacking from the rear of his opponent after going over mountains or by luring his opponents up onto mountains after him.<p>But really both light and heavy cavalry were important parts of the regular Mongol forces as well as the hordes of arrow-fodder they would levy from captured cities.  And while the Mongols didn&#x27;t start out with much in the way of a siege train they had the world&#x27;s best siege engineers by the time they finally finished off the Jin dynasty.<p>The hot, wet environment of India was a big barrier to their expansion as was their navel weakness.  But Europe benefited mostly by being so far away and from the fact that the Mongols hadn&#x27;t finished off the Song by the time the empire started to fragment.<p>Sources: A number of things over the years but I recently finished <i>Genghis Khan: His Conquests, His Empire, His Legacy</i>.