The Mongol Empire was founded by Temujin, also known as Genghis Khan, and was the largest continuous empire ever.

From Wikipedia:

The Mongol Empire, also known as the Mongolian Empire (Mongolian: Монголын Эзэнт Гүрэн, Mongolyn Ezent Güren; 1206–1405) was the largest contiguous empire in world history and for some time was the most feared in Eurasia. It was the product of Mongol unification and Mongol invasions, which began with Temujin being proclaimed ruler in 1206, eventually sparking the conquests.By 1279, the Mongol Empire covered over 33,000,000km² (12,741,000sqmi),[1] up to 22% of Earth's total land area. It held sway over a population of over 100 million people. However, by that time the empire had already fragmented, with the Golden Horde and the Chagatai Khanate being de facto independent and refusing to accept Kublai Khan as Khagan.[2][3] By the time of Kublai Khan's death, with no accepted Khagan in existence, the Mongol Empire had already split up into four separate khanates.During the beginning of the 14th century, most of the khanates of the Empire gradually broke off. They went on to be absorbed and defeated.

The Mongolian Empire is loosely referenced throughout book 1. The primary reference is to the Golden Horde, which was a khanate of the greater Mongolian Empire after the death of Genghis Khan. Robinson references to the Mongolian Empire on page 65, when Kyu is speaking to Zheng He looking to get acceptance into the imperial palace. Robinson is mentioning the empire because it was one of the primary reasons Zheng He's fleet was grounded. This is because there is no way for the expensive fleet to move against their most prominent enemy and the funds used to manage the fleet could be diverted elsewhere better from the emperor's heirs point of view.