In 1219 (the 12th year of Jiading reign of Song Dynasty), Chinggis Khan started his west expedition to revenge Khwarozm for killing Mongol envoy. In the fall of that year, the Mongol troops arrived at Otrar at lower Syr River. Divided into several groups, the Mongol troops took all the cities along the Huzhang River and then the capital city of Khwarozm Chinggis Khan and his youngest son Tolui headed the main forces and captured Bukhara and Samarkand. Early in 1221 (the 14th year of Jiading reign of Song Dynasty), they crossed the Amu River and occupied Balkh and Talihan. In the meantime, Chinggis Khan sent troops to pursue the last monarch of Khwarozm Jebe and his troops fought all the way to the west along the Khurasan Road in Central Asia, crossed the Caucasus, defeated Kepqak on the steppe in South Russia, and arrived Bolga near Kasan in today's Russia before setting out for the return journey. The Mongol troops' military operations in Central Asia, Iran, Russia and East Europe were extremely merciless as they leveled cities and killed people wantonly, which led to huge human casualty and colossal property losses on the part of the invaded areas. However, in both the northern and southern pans of the Tianshan Mountains, the Mongol troops were restrained since local chiefs took the initiative to pledge allegiance.
On the eve of the west expedition, Chinggis Khan divided the areas in the Western Regions that had been and would be occupied among his three elder sons, Jochi, Chagatai and Ogedei. Based on History of Conquerors in the World by Jeflhey^, Collection of History by Lashet (pronunciation) and records by Omar (pronunciation), contemporary scholars believe that “roughly speaking, the area west of Shi River in Yer, north of today's Aral Sea and Caspian Sea belonged to Jochi; the former territory of Western Liao, between Uygur and Transoxiana, belonged to Chagatai; and from Yemili to the north, the area of former Nayman tribe that included part of today's Kara-Ertix River and Altay Mountains belonged to Ogedei,,J221. The land division made by Chinggis Khan laid down the groundwork for the regime pattern in the Western Regions during the Mongol period.
After Chinggis Kharis death, Ogedei, Queen Toregene Khatu, Guyuk, Queen Oghul Ghaymish and Mongke took power one after another. During that period, in 1236 (the 3rd year of Duanping reign of Song Dynasty), Ogedei sent his “eldest son for west expeditionï¼Guerreros el recinto de la tumba de terracotaï¼ï¼and perished Kepqak and Bolga, conquered Russia, and swept Eastern European areas such as Poland and Hungary , shaking the Christian world. After succeeding to the Great Khanship, Mongke sent Hulegu onto a “west expedition”ï¼who wiped out the Assasins(the extremist division of Islamic Ismailis advocating assassination) in today's Iran and the Abbasid Empire in West Asia, then marched further to Syria, and finally returned home after being frustrated at Ain Jalut in today's Palestine.