The boy Temujin was born of a Mongol chief around 1167 north of the Gobi desert. Through bitter struggle he removed all rivals, notably the tribe of Tartars, whose name East and West would adopt for the united hordes Temujin gathered in 1206. They proclaimed him Genghis Khan, master of 'all the people with felt tents', and China was but the first to suffer his fury. After the Khorezmshah's governor at Otrar slaughtered a Mongol merchant caravan in 1218, Genghis dispatched three envoys to Mohammed's court. When Mohammed killed one and burnt the others' beards, he sealed his fate. Contemporary historian Juvaini hardly exaggerates the result: "For every drop of their blood there flowed a whole Oxus; in retribution for every hair on their heads, it seemed that a hundred thousand heads rolled in the dust at every crossroads."
The Mongol horsemen were deadly archers, able to ride for days and nights on end, sleeping in the saddle, nourished by the blood of their steeds. Strategies like the feigned retreat overcame numerical inferiority, while massed ranks of Sogdian prisoners formed protective walls from enemy arrows.
Mongol forces marched on the Kara-Khitan Khanate, and by 1218 controlled territory as far west as Lake Balkhash in the southeast of what is now Kazakhstan. Genghis Khan initially looked towards the Khwarezmid Empire as a trading partner, but when his mercantile caravan was slaughtered and a subsequent envoy killed, battle lines were drawn. With 200,000 troops under his command, he marched across the Tian Shan Mountains and into the heart of Uzbekistan.
The Mongols first seized Otrar, murdered many of its inhabitants and enslaved the rest. Inalchuq, the governor responsible for the previous envoys demise, had molten silver poured into his eyes and ears as punishment. In quick succession Mongol forces seized and decimated Samarkand and Bukhara, leaving them as virtual ghost towns. Pyramids of severed heads were raised as a sign of victory. In Termez the entire population was killed, and perhaps a million people were slaughtered in a bloodbath in Urgench.
By 1221 Genghis Khan's domains spread from China to the Caspian and the grand cities of Central Asia lay in ruin. His successors pushed even further, simultaneously challenging the Japanese and the Germans from the greatest land empire the world has ever seen.
Their campaigns left some five million dead, yet in their wake the Mongols established the Pax Mongolica, over a century of stability and recovery of which Marco Polo was a witness and beneficiary. As the уam horse relay system speeded communications to a level surpassed only by 19th century engineers, the Silk Road traveller could march with impunity "from the land of sunrise to the land of sunset with a golden platter upon his head". Before his death in 1227, the Great Khan divided his realm between his four sons. Most of Uzbekistan fell within the ulus of Chagatai, his second son. Initial hostility to Islam laded as subsequent rulers adapted to local Turkic culture and by the 14th century their language was known as Chagatai Turkic. Fragmentation of power sparked wars among various fiefs, brilliantly exploited by the Turkicized Mongol Tamerlane.
The Mongol invasion was a turning point for central Asia in numerous ways: it broke Islamic hegemony, replacing it with a Turkic identity; it razed cities to the ground, destroying any pre 13th-century architecture; and it gave the regions population much of the genetic make-up it has today.