The success of Genghis Khan and the Mongol Empire was perhaps due to the fortunate occurrence of abundant rain in the area for 15 years, according to National Geographic. The region suffered through extreme drought conditions in the 1180s and 1190s, but then unusually warm and rainy weather entered Mongolia from 1211 to 1225, a conclusion based upon tree ring samples taken by scientists.
The good weather allowed Mongol herdsmen to raise more horses. Camels, yaks, cattle and sheep were also raised very quickly due to grass grown during the wet periods. The charismatic leader united the Mongols after the chaotic droughts and efficiently moved his army over the steppes of his country. Horses became the backbone of Khan's cavalry, and livestock provided meat and clothing for his soldiers.
Scientists determined that 15-year spell of warmth and precipitation had not been seen in that region for more than 1,000 years before that time period, and those conditions have not happened since. Abundant resources, combined with Khan's leadership, new technologies and a large army, contributed to his success as a commander. Geography did play a role in that his people had a lot of resources to expend for a drawn-out conquest. Khan's descendants ruled parts of the world until the 1920s, more than 700 years after his death.