An empire that spans a continent needs a single will at its center. After 1259 the Mongol Empire lost one. Within a few years it had split into four great realms, each ruled by a different branch of Chinggis's family, and often at war with the others.

Brothers at war

When Mongke died, two of his brothers claimed the throne. Kublai, campaigning in China, was proclaimed by his own supporters in 1260. His youngest brother, Ariq Boke, was proclaimed at Karakorum by a rival assembly. The civil war between them lasted until 1264 and was decided largely by supply: Kublai controlled the grain of northern China, and Karakorum depended on it. Ariq Boke surrendered. But many princes never accepted Kublai, whom they saw as too Chinese, and his cousin Kaidu, a grandson of Ogedei, fought him in Central Asia for decades. Kaidu's long war was not only personal: it pitted a steppe-centered vision of empire against Kublai's China-centered one.

The four realms

By the late 1260s four khanates had emerged. In the east, Kublai ruled China and Mongolia as the Yuan dynasty. He also kept a summer capital at Shangdu, the Xanadu of later English poetry, where the court moved each year to hunt and to stay close to the steppe. In Iran and Iraq stood the Ilkhanate, founded by Hulegu; the title Ilkhan meant a subordinate khan, a sign that he acknowledged Kublai's seniority. In the western steppe, Jochi's descendants ruled the Golden Horde, also called the Ulus of Jochi or the Kipchak Khanate, which dominated the Rus principalities from its capital at Sarai, on the lower Volga. Its Mongol rulers were few; most of its people were Kipchak Turks, and Turkic soon replaced Mongolian as the everyday language. In Central Asia, the descendants of Chagatai ruled the Chagatai Khanate. The Chagatai khans, closest to the old nomadic life, governed the oasis cities of Transoxiana from the saddle and were the slowest to adopt the settled ways of their subjects.

The split showed first in war between Mongols. Berke, khan of the Golden Horde, had converted to Islam, and he was angered by Hulegu's sack of Baghdad. Rivalry over the rich pastures of Azerbaijan mattered too. In 1262 the two khanates fought the first open war between Mongol realms. Berke even allied with the Mamluk sultanate of Egypt, the Ilkhanate's enemy. Religion and local interests were already pulling the family apart.

Kublai's China

Kublai completed the conquest of the Song in the 1270s; the last Song loyalists perished at sea in 1279. For the first time since the Tang, all of China was united, under a foreign ruler. Kublai governed through a mix of Mongol, Chinese and foreign officials. The Yuan sorted people into broad categories, with Mongols at the top, then semuren from Central and Western Asia, whose name means "people of various kinds," then northern Chinese and finally southern Chinese. How strictly this ranking worked in practice is debated, but southerners were clearly disadvantaged, and the examination system was suspended until 1315. The Yuan relied heavily on paper money, which visitors from the west found astonishing; later overprinting fed inflation.

Kublai's overseas ventures went badly. He sent fleets against Japan in 1274 and 1281. Both failed, the second when a typhoon wrecked a huge fleet. The Japanese later called such storms kamikaze, "divine winds." Armies sent against Dai Viet, in what is now northern Vietnam, were repelled; in 1288 the Vietnamese general Tran Hung Dao destroyed a Mongol fleet by planting stakes in the bed of the Bach Dang River. An expedition to Java in 1293 also ended in retreat. The limits of a horse empire were showing at sea and in the tropics.

The Ilkhanate turns to Islam

The early Ilkhans favored Buddhists and Christians, and some hoped for an alliance with Christian Europe against the Mamluks. That changed in 1295, when Ghazan converted to Islam on taking the throne. Most Mongols in Iran followed, and the dynasty increasingly governed as a Persian Muslim monarchy. Ghazan's vizier, Rashid al-Din, reformed taxes and began his great world history. Converting brought rulers closer to the people they ruled, and over time the Mongols of Iran, Central Asia and the Golden Horde were absorbed into the Turkic and Persian Muslim societies around them. Conquerors who had arrived as outsiders became, within a few generations, part of the local landscape.

Worked example: whose empire?

Ask "When did the Mongol Empire end?" and you can get several defensible answers. A historian focused on unity might say 1260, when the civil war began, or 1264, when no single khan was obeyed everywhere. A historian of China might say 1368, when the Yuan was driven out. A historian of Russia might point to 1480, and a historian of Crimea to 1783. Each answer reflects a different definition of "the empire": a single state, a family enterprise, or a political tradition that outlived both. Before you argue about an answer, define the question. That habit clears up many historical debates that turn out to be disagreements about words.