Original: He was elected supreme khan in 1229, according to the kurultai held at Kodoe Aral on the Kherlen River after Genghis' death, although this was never really in doubt as it was Genghis' clear wish that he be succeeded by Ögedei.
Simplified: After Genghis Khan's Death He was selected as the supreme khan in 1229 because of the kuriltai held after Genghis' death, but it was never doubted that Genghis wanted Ögedei to rule after him.