During the reign of the successor of Genghis Khan, Ogodei Khan (d.1240/41), the Jochid Ulus or realm greatly expanded in size. In 1237, Jochi's son Batu (1227-1255), assisted by the famous Mongol general Subedei, led a large army westward. In route they destroyed the Bulgar khanate on the Volga River, pacified the numerous Turkic tribes of the steppes, and conquered the Russian cities. Then in 1240, Mongol armies invaded Hungary and Poland, winning victories over the knights of Europe at Mohi in Hungary and Liegnitz in Poland. As news spread of the ferocity of the Mongols, Europe trembled in anticipation of an attack that never came. In 1241 Ogodei Khan died, which forced the Mongol armies to withdraw to Russia in order to elect a new khan.
Despite an intense rivalry with Güyük Khan, Ogodei's son, Batu established the Golden Horde as a semi-independent part of the Mongol Empire. The origins of the name Golden Horde are uncertain. Some scholars believe that it refers to the camp of Batu and the later rulers of the Horde. In Mongolian, Altan Orda refers to the golden camp or palace. Altan (golden) was also the color connoting imperial status. Other sources mention that Batu had a golden tent, and it is from this that the Golden Horde received its name. While this legend is persistent, no one is positive of the origin of the term. In most contemporary sources, the Golden Horde was referred to as the Khanate of the Qipchaq as the Qipchaq Turks comprised the majority of the nomadic population in the region (the Ulus Jochid).
Batu died in 1255, and the next significant ruler was his brother Berke (1255-1267) who had converted to Islam and focused most of his energies against the Il-Khans of Persia. His conversion marked the first time an important leader among the Mongols abandoned the traditional shamanistic religion. Hulegu, the founder of the Mongol Il-Khanate, had sacked Baghdad in 1258 and killed the Caliph of Islam. Berke forged an alliance with the Mamluks of Egypt who were also enemies of the Il-Khans. The war with the Il-Khans lasted until the final collapse of the Il-Khanate in 1334.