When Chinggis Khan died, his empire stretched from northern China to the Caspian. Thirty years later his sons and grandsons ruled from Korea to Hungary and from Siberia to the Persian Gulf, the largest contiguous land empire the world had yet seen. The expansion was driven by an idea as much as by appetite: many Mongols came to believe that Eternal Heaven had granted their khan dominion over the whole earth, so any ruler who refused to submit was a rebel.

Ogedei and Karakorum

Chinggis had chosen his third son, Ogedei, as his successor, judging him more even-tempered than his older brothers Jochi and Chagatai, who quarreled bitterly. A kurultai confirmed Ogedei in 1229. He built a capital at Karakorum in the Orkhon valley, where envoys, merchants and captive craftsmen gathered. With the help of advisers such as Yelu Chucai, a Khitan scholar, the Mongols began collecting regular taxes in northern China instead of simply plundering it. Yelu Chucai is said to have talked Ogedei out of a proposal to empty northern China of farmers and turn it into pasture, by showing how much revenue farmers could pay. The story comes from his admirers, but the shift toward taxation was real. In 1234 Mongol and Song forces destroyed the Jin dynasty together.

The western campaign

In 1235 a kurultai launched campaigns in several directions at once. The most famous went west, led by Batu, guided by Subutai as chief strategist. Batu was Jochi's son. In the winter of 1237 the army used frozen rivers as highways and attacked the Rus principalities, which were divided and quarrelsome. Ryazan and Vladimir fell, and in 1240 the Mongols sacked Kiev, chief city of the Rus. A papal envoy who passed through a few years later reported countless skulls and bones lying in the fields.

In 1241 the Mongols moved into Poland and Hungary. On April 9 one army defeated Polish and German knights at Legnica. Two days later the main force destroyed the Hungarian army of King Bela IV at Mohi. Mongol riders reached the Adriatic coast. Then, in 1242, they withdrew. Historians still debate why. The traditional explanation is news that Ogedei had died in December 1241, which drew the princes home to take part in choosing a successor. Others point to the limited pasture of the Hungarian plain, wet weather that turned the land to marsh, heavy losses, or a plan that had always been a raid. The question is open. Whatever the reason, central Europe was spared another invasion on that scale, although Mongol armies raided Poland and Hungary again later in the century.

Succession struggles

Every Mongol succession was contested, because many descendants of Chinggis could claim the throne. Toregene, Ogedei's widow, ruled as regent from 1241 to 1246 and secured the election of her son Guyuk. The Franciscan John of Plano Carpini attended Guyuk's enthronement in 1246 and carried home a letter, which survives in the Vatican archives, demanding that the pope come in person to offer submission. Guyuk's reign was brief; he died in 1248, possibly on his way to confront his cousin Batu. Then power swung to another branch. Sorghaghtani Beki, widow of Chinggis's youngest son Tolui, had spent years building alliances. One medieval chronicler wrote that if he found another woman like her, he would have to call women superior to men. In 1251 the assembly elected Mongke, son of Sorghaghtani, as Great Khan, and supporters of the Ogedei line were purged.

Mongke's grand plan

Mongke was a capable administrator who ordered censuses across the empire and tried to standardize taxes. He sent his brother Kublai against the Song in southern China and his brother Hulegu against Iran and the Middle East. Hulegu destroyed the fortresses of the Nizari Ismailis, the sect Europeans called the Assassins, taking their stronghold of Alamut in 1256. In 1258 he sacked Baghdad and ended the Abbasid caliphate. Mongke himself led an army into southwestern China, where he died in 1259 during the siege of a mountain fortress at Diaoyu, probably of disease. His death, like Ogedei's, stopped campaigns in their tracks and set off a crisis.

Worked example: the friar at Karakorum

In 1253 a Flemish Franciscan, William of Rubruck, set out for Mongke's court. He carried a letter from King Louis IX of France, but he was not a formal ambassador. At Karakorum he found a town with a Muslim quarter, a Chinese quarter, mosques, Buddhist temples and a Nestorian church, along with a Parisian goldsmith named Guillaume Boucher, who built a silver tree that poured drinks from its branches. In 1254 Mongke staged a debate among rival religions: Latin and Nestorian Christians, Muslims and Buddhists. In Rubruck's telling the debate was lively and ended in drinking rather than conversion, and Mongke told him that the Mongols believed in one God but that, as the hand has several fingers, God gave people several ways. Rubruck's account shows both the openness of the Mongol court and its firm expectation that every ruler, Louis included, would eventually submit.