Genghis Khan was born around 1162 under the name Temüjin in the area around Lake Baikal in modern day Mongolia. He was the son of Yesügei, the chief of the Kiyad tribe, and his mother Hoelun was from the Olkhunut tribe. At age 9, his father took him to live with the family of his future wife Börte. However, Yesügei was poisoned soon after while en route back home, leaving the family abandoned.


Temüjin and his family led a tough life for many years, living in poverty and relying on charity while he was still a boy. Several years later, Temüjin killed his older half-brother Begter for hoarding food and disobeying their mother. This act helped earn Temüjin authority despite his youth. Around 1178, Temüjin married Börte as previously arranged. However, she was soon kidnapped by the rival Merkit tribe shortly after and Temüjin had to rescue her with the help of his ally and future rival Jamukha.


Over the following years, Temüjin began building a power base among the Mongol tribes, attracting followers and building military strength. Many tribal leaders agreed to submit to his leadership after being defeated. His main rivals were Jamukha and Toghrul, the Kerait leader who had helped Temüjin rescue Börte years earlier. After growing conflicts with both rivals, Temüjin defeated them in 1203 and 1204 respectively to become the sole prominent leader among the Mongols.


In 1206, Temüjin formalized his leadership by founding the Mongol Empire. A great assembly or kurultai proclaimed him as the supreme leader and conferred upon him the new title of Genghis Khan, meaning “universal ruler”. He established a meritocratic method of organization and codified the rule of law among the previously fragmented tribes. Setting up his capital at Avarga near the Onon and Kherlen rivers, Genghis Khan initially focused his efforts against traditional Mongol rivals like the Naiman and Merkits to the west.


Genghis then aimed at the powerful Xia and Jin dynasties ruling northern China, correctly judging them to be economically and politically fragile. Starting in 1211, the Mongols invaded the Jin state, taking advantage of political turmoil to sweep through and capture numerous cities. The sudden departure of Genghis from the frontline to attend to the accidental death of his son Jochi helped halt the campaign. When it resumed from 1213-1214, the Mongols used superior strategy and mobility to annihilate the 500,000 man Jin army near Beijing in 1215.


Another child of Genghis, Ögedei was designated as the successor after proving himself on this campaign. The victory provided the Mongols control of the area around Beijing and enormous war booty while spreading terror at their name. Further rapid attacks against the Xia dynasty delivered more territorial gains for a Mongol nation that now bordered southern Siberia to the north and Tibet and the Yellow River basin from the west to south.


The destruction of Khwarezmia in Central Asia would mark the next phase of conquests under Genghis Khan. Its ruler had Governor Inalchuq of Otrar attacked and looted a commercial caravan sent by Genghis Khan in 1218 in defiance of treaties established. This fateful decision ignited retaliation from Genghis, who pronounced to his generals, “Will we too become servants of the Khwarezm Shah?”


Genghis quickly gathered experienced generals and a large army that may have totaled as many as 200,000 warriors for the upcoming campaign. The Mongols swept away Khwarezm’s defenses despite their previous unfamiliarity with siege warfare, circumventing fortified cities when possible and depending on urban Muslim merchants to help breach settlements. When Samarkand, Bukhara and other major cities offered resistance, the Mongols responded with a level of carnage and terror unseen anywhere before in the Islamic world.


However, the Khwarezm Shah escaped this...