the united Mongol Empire in 1206. The Mongols would proceed to conquer the majority of modern East Asia. Meanwhile, China were divided into five competing states. From 1211, Mongol forces invaded North China. In 1227 the Mongol Empire conquered Western Xia. In 1234, Ogedei Khan extinguished the Jin dynasty. The northern part of China was annexed by Mongol Empire. In 1231, the Mongols began to invade Korea, and quickly captured all the territory of the Goryeo outside the southernmost tip. The Goryeo royal family retreated to the sea outside the city of Seoul to Ganghwa Island. Goryeo was divided between collaborators and resisters to the invaders. However, at the time, the Goryeo Sannotei on the peninsula resisted until 1275. In the 1250s, the Mongols invaded the last remaining state in southern China – the Southern Song. The invasion carried on for over thirty years, and likely resulted in millions of casualties. In 1271, Kublai Khan proclaimed the Yuan dynasty of China in the traditional Chinese style. The last remnants of the Song were defeated at sea in 1279. China was unified under the Yuan dynasty. Kublai Khan and his administration shifted to the Central Plains area and embraced Confucianism. By 1275, Goryeo had surrendered to the Yuan dynasty as a vassal. Members of the Goryeo royal family were raised to understand Mongol culture, and intermarried with the Yuan imperial family. Japan was seriously threatened by the Yuan forces from the East Asian mainland. In 1274, Kublai Khan appointed Yudu. In order to recruit Marshal Dongdu to command the Yuan forces, Han Bing and the Goryeo army began the first expedition to Japan. The Yuan dynasty invaded Japan in two separate invasions, both of which were disrupted by natural typhoons. These two invasions both occupied the town of Kitakyushu before being swept into the sea. At the time the Yuan dynasty fleet was the largest fleet in the history of the world. In order to cope with the nationwide mobilization of the powerful Yuan army, Japan's economy and military were placed under severe pressure. The Japanese Kamakura Shogunate had difficulty compensating its soldiers who had defended the country, which intensified the contradiction between the domestic warrior groups. The ruling system collapsed in the first half of the 14th century. Science and Technology Gunpowder Most sources credit the discovery of gunpowder to Chinese alchemists in the 9th century searching for an elixir