After unifying the country, Kublai Khan, who became emperor, began to demand that all neighboring countries submit to the Yuan Dynasty.
However, the Goryeo Dynasty, which was already garrisoned by the Mongols on the small island of Ganghwa, was often in rebellion.
In 1258, Gojong of the Goryeo Dynasty submitted to Kublai Khan and sent the crown prince as a hostage to the Yuan court. Kublai Khan, after succeeding him as Great Khan, made the prince of Goryeo his son-in-law and sent him back to Goryeo to rule his country.
Since then, the Yuan Dynasty and the Goryeo Dynasty have established friendly relations through marriage.
In 1268 and 1271, Kublai Khan first demanded Japan's allegiance to the Yuan Dynasty twice, but both were rejected by Hojo Toshimune, the eighth ruler of the Kamakura shogunate.
In 1274, Kublai Khan sent a fleet of 150 ships to begin an expedition to Japan, and the Mongol army captured the Falklands and Iki Islands, landing at Juzaki Bay in Kyushu.
But the steppe cavalry were not accustomed to such a sea expedition. And they saw themselves as the core of the invading army, and the main body of the army was an auxiliary army composed of war-weary Han and Goryeo people.
After repelling the defenders on the shore with artillery fire, the Yuan army began to advance inland. Under the stubborn resistance of the daimyōs of Kyushu, they were forced to retreat to the battleships.
In 1276, Kublai Khan demanded Japan's allegiance to the Yuan Dynasty for the third time, but hojo shimō refused.
In June 1281, after a long period of preparation, Kublai Khan sent a fleet of 45,000 Mongols, 120,000 Han and Goryeo to land at Eagle Island and Heilo in Juzaki-mae Province, Kyushu.
This time, although well prepared, they still did not defeat the Japanese, and a terrible hurricane suddenly struck on August 15, 1281, destroyed the Mongol fleet, leaving them without a base, after which the Mongol army was either killed or captured.
At the same time, however, Kublai Khan's war in Indochina was not optimistic.
The region was then divided into four countries, namely the Annam Kingdom influenced by Chinese culture, the Champa State of Malaya-Polynesians influenced by Indian culture, the State of Cambodia established by the Pure Khmer People influenced by Indian culture, and the State of Burma founded by a Tibetan from Burma who believed in Brahmanism and Buddhist culture.
In 1280, the Champa king Dravidian succumbed to the obscenity of Kublai Khan's emissaries and was forced to recognize the suzerainty of the Yuan Dynasty, but the people of the country refused to submit.
In 1283, Kublai Khan sent a small group of soldiers and horses led by Suke Bald to capture the champa capital of the Buddha Oath, and was subsequently driven back to the ship by the Champa guerrillas.
In 1285, Kublai Khan sent his son Dehuan to lead a large army into Indochina and cross the Tokyo Plain through Mount Lang to attack Annam.
Although Dehuan won a victory near the northern part and continued to attack Hanoi, he was defeated by the Annam people at The Sheng Long in the delta, and was forced to retreat back to China in desperation.
Meanwhile, The Seko Bald attempted to attack Annan from behind in the south, but was attacked by the Annans in Therkit Bay and killed by them.
In 1287, Kublai Khan, who was not willing to be defeated, once again sent an army to attack Annam. Although this Mongol army captured Hanoi, it was unable to hold it, and under the stubborn resistance of Chen Renzong, the king of Annam, they once again scattered the city. Chen Renzong returned to the capital in victory.
The following year, however, he was the norm and wisely acknowledged the suzerainty of the Yuan Dynasty.
Subsequently, the Champa state also voluntarily submitted to the Yuan Dynasty and fulfilled the obligations of subjection.
In 1277 the Mongols seized the Bamo Strait in Burma and controlled important routes into the Irrawaddy River basin.
After two wars, they captured the Burmese capital of Bagan in 1287.
In 1297, the new Bagan king Qiao Rong recognized the suzerainty of the Yuan Dynasty. In 1300, disputes arose within Burma over the succession to the Bagan throne, and the Mongols once again intervened in Burmese affairs to maintain order.
In 1296, Kublai Khan's successor, Timur the Great, sent a mission to Cambodia.
From 1294 onwards, the two Thai kingdoms of Chiang Mai and Suogutai (陳古泰) also recognized the suzerainty of the Yuan Dynasty.
In 1293, Kublai Khan sent an expeditionary force of 30,000 from Quanzhou to attack Java. At that time, the kingdom of Java was under the rule of King Jayiri in the eastern part of Java.
The Yuan dynasty generals Shi Bi and Gao Xing led their troops, with the help of another Javanese governor, Hambiye, and captured the capital city of Yuyili.
However, before they could stabilize, they were attacked by Tuhanbiye and driven out of Java.
After liberating the island of Java, Tuhanbiya established the majapahit state.