Before his death, Jenghiz had recommended his third son, Ogedey (Oktay) to become the ruler. Ogedey obeyed to this rule in the course of the Grand Assembly that gathered in the year of 1228 and he was selected as the khan and enthroned by his brother, Chagatai. In the period of Ogedey, Korea was annexed, and the entire northern China was connected to the empire. In the course of the western expedition that took place in the years of 1237-1241, Russia and the entire eastern Europe were invaded.
Pursuant to the death of Ogedey, the state was administered by his wife, Toregene until the selection of a new khan. Toregene provided the enthronement of his son, Guyuk as the khan despite the opposition of Batu in the Grand Assembly of 1246. This movement nearly caused an armed fight between Coci's son, Batu who was the victorious commander of the western armies and Guyuk. Upon the death of Guyuk (1248), the public order was established. Pursuant to the state administration by his wife, Ogul Gaymis as a regent for three years (1248-1251), the sovereignty passed to the lineage of Jenghiz's young son, Toluy. The election of Toluy's son, Mungge as teg khan (1251/52) pleased both parties any conflicts and fights were prevented thereof. Mungge wanted to continue the works that were initiated by Jenghiz and partially followed in the period of Ogedey and he intended to complete these works. To this effect, he dispatched large armies from two directions one towards the southern China and the other towards the Middle East. Thus, he undertook to apply his plan. The leader of the armies in China was his brother, Hubilay (Kubilay), and the leader of the forces sent towards the Middle East was his little brother, Hulagu. According to the ancient tradition, the state was considered as the property of the dynasty. Therefore, Jenghiz had shared various regions among his sons in his lifetime and entitled with the right to execute and get the benefit of it.
Accordingly, his elder son, Coçi (Cuçi, Cuci) had taken the north-west, in other words, the Kipchak country; Chagatai had taken Turkestan; Ogedey had taken the western regions and his younger son, Toluy had stayed in the main homeland in order to maintain the imperial lineage. As long as the khanate was strong and powerful, Jenghiz's sons had been loyal to the central government and they administered their countries like a governor. However, when the central government lost power, the parts of the empire had been divided into 4 sections in accordance with the geopolitical and cultural centres such as 1) Chin Yuan tribe that emerged from Hubilay (Kubilay) (its centre, Mongolia was included in this section), 2)Turkestan under the government of Chagatai's sons, 3) the Golden Horde state under the dominion of Cuci's (Çoçi) sons and Ilhanli State under the dominion of Hulagu family.