Genghis Khan
Kurultai of 1206 and reforms

Now sole ruler of the steppe, Temüjin held a large assembly called a kurultai at the source of the Onon River in 1206. Here, he formally adopted the title Genghis Khan, the etymology and meaning of which have been much debated. Some commentators hold that the title had no meaning, simply representing Temüjin's eschewal of the traditional gurkhan title, which had been accorded to Jamukha and was thus of lesser worth. Another theory suggests that the word "Genghis" bears connotations of strength, firmness, hardness, or righteousness. A third hypothesis proposes that the title is related to the Turkic tängiz ('ocean'), the title "Genghis Khan" would mean "master of the ocean", and as the ocean was believed to surround the earth, the title thus ultimately implied "Universal Ruler".

Having attained control over one million people, Genghis Khan began a "social revolution", in May's words. As traditional tribal systems had primarily evolved to benefit small clans and families, they were unsuitable as the foundations for larger states and had been the downfall of previous steppe confederations. Genghis thus began a series of administrative reforms designed to suppress the power of tribal affiliations and to replace them with unconditional loyalty to the khan and the ruling family. As most of the traditional tribal leaders had been killed during his rise to power, Genghis was able to reconstruct the Mongol social hierarchy in his favour. The highest tier was occupied solely by his and his brothers' families, who became known as the altan uruq (lit. 'Golden Family') or chaghan yasun (lit. 'white bone'); underneath them came the qara yasun (lit. 'black bone'; sometimes qarachu), composed of the surviving pre-empire aristocracy and the most important of the new families.

To break any concept of tribal loyalty, Mongol society was reorganised into a military decimal system. Every man between the age of fifteen and seventy was conscripted into a minqan (pl. minkad), a unit of a thousand soldiers, which was further subdivided into units of hundreds (jaghun, pl. jaghat) and tens (arban, pl. arbat). The units also encompassed each man's household, meaning that each military minqan was supported by a minqan of households in what May has termed "a military–industrial complex ". Each minqan operated as both a political and social unit, while the warriors of defeated tribes were dispersed to different minqad to make it difficult for them to rebel as a single body. This was intended to ensure the disappearance of old tribal identities, replacing them with loyalty to the "Great Mongol State", and to commanders who had gained their rank through merit and loyalty to the khan. This particular reform proved extremely effective—even after the division of the Mongol Empire, fragmentation never happened along tribal lines. Instead, the descendants of Genghis continued to reign unchallenged, in some cases until as late as the 1700s, and even powerful non-imperial dynasts such as Timur and Edigu were compelled to rule from behind a puppet ruler of his lineage.

Genghis's senior nökod were appointed to the highest ranks and received the greatest honours. Bo'orchu and Muqali were each given ten thousand men to lead as commanders of the right and left wings of the army respectively. The other nökod were each given commands of one of the ninety-five minkad. In a display of Genghis' meritocratic ideals, many of these men were born to low social status: Ratchnevsky cited Jelme and Subutai, the sons of blacksmiths, in addition to a carpenter, a shepherd, and even the two herdsmen who had warned Temüjin of Toghrul's plans in 1203. As a special privilege, Genghis allowed certain loyal commanders to retain the tribal identities of their units. Alaqush of the Ongud was allowed to retain five thousand warriors of his tribe because his son had entered into an alliance pact with Genghis, marrying his daughter Alaqa.

A key tool which underpinned these reforms was the expansion of the keshig ('bodyguard'). After Temüjin defeated Toghrul in 1203, he had appropriated this Kereit institution in a minor form, but at the 1206 kurultai its numbers were greatly expanded, from 1,150 to 10,000 men. The keshig was not only the khan's bodyguard, but his household staff, a military academy, and the centre of governmental administration. All the warriors in this elite corps were brothers or sons of military commanders and were essentially hostages. The members of the keshig nevertheless received special privileges and direct access to the khan, whom they served and who in return evaluated their capabilities and their potential to govern or command. Commanders such as Subutai, Chormaqan, and Baiju all started out in the keshig, before being given command of their own force.
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