Under Kublai Khan the Mongol empire reached its largest extension. He ruled over 24000000 km² (nearly 10000000 mi²). The empire went from China and Korea to Iran and southern Russia, from the Korean peninsula to the Danube River.
During Kublai's reign the empire was divided into four smaller Kanatos but he still remained as the Great Khan of all of them. He was actually the first Khan to successfully conquest China in 1279, making him the first Yuan ruler of the whole China. After his death, the mongols didn't elect a new Khan and the Kanatos became more independent.
Everything from California to Alaska and between the Rocky Mountains and the Pacific Ocean was a British-held territory called Oregon. The trail pointed the way for the United States to expand westward to achieve what politicians of the day called its “Manifest Destiny” to reach “from sea to shining sea.”
