Möngke conducted a brutal purge of the Ögedeid and Chagatai families, whom he saw as rivals. Kaidu’s father, Kashin, had already died, but Kaidu himself was spared due to his youth and obscurity. However, he was placed under close surveillance. According to The Secret History of the Mongols , the young prince was assigned a small, impoverished appanage in the remote Emil River valley (modern-day eastern Kazakhstan). It was a deliberate insult—a barren, rocky region incapable of supporting a large army. But it was here that Kaidu forged his character. He learned patience, honed his skills in riding and archery, and began quietly building a network of loyal followers among the discontented clans. The memory of the Toluid usurpation and the humiliation of his family never left him. The death of Möngke Khan in 1259 triggered the great Toluid Civil War between his brothers: Kublai (who favored Chinese-style sedentary rule) and Ariq Böke (who championed Mongol traditionalism). Kaidu shrewdly supported Ariq Böke, seeing a chance to restore Ögedeid power. Although Ariq Böke lost in 1264, Kaidu emerged not as a defeated vassal, but as a defiant warlord. He refused to appear at Kublai’s new capital, Khanbaliq (modern Beijing), to swear fealty.
His key ally was his cousin, , the Khan of the Chagatai Khanate, who provided the heavy cavalry and settled resources of Transoxiana. Together, they launched annual invasions into Kublai’s territory, often reaching as far east as Karakorum, the old Mongol capital. The Struggle for the Nomadic Soul Kaidu’s war was not merely dynastic; it was ideological. He saw Kublai’s adoption of Chinese court rituals, paper money, fixed taxes, and a bureaucratic state as a betrayal of Genghis Khan’s Yassa (law). In Kaidu’s eyes, a Mongol should live in a felt tent ( ger ), follow the herds, and owe allegiance only to a khan who proved himself on horseback. He famously declared: “Kublai has polluted himself with the customs of the peasants. Our grandfather’s empire was won with the bow and the horse, not with brushes and ink.” Möngke conducted a brutal purge of the Ögedeid
But Duwa, pragmatic, made peace with Temür Khan shortly after. Kaidu’s realm was divided, and his descendants were eventually absorbed or destroyed. According to The Secret History of the Mongols