The repulsions of two Mongol invasions were momentous events in Japanese history. Japanese relations with China had been terminated in the mid-ninth century after the deterioration of late Tang China and the turning inward of the Heian court. Some commercial contacts were maintained with southern China in later centuries, but Japanese pirates made the open seas dangerous. At a time when the bakufu had little interest in foreign affairs and ignored communications from China and Koryo (as Korea was then known), news arrived in 1268 of a new Mongol regime in Beijing. Its leader, Khubilai Khan, demanded that the Japanese pay tribute to the new Yuan Dynasty (1279-1368) and threatened reprisals if they failed to do so. Unused to such threats, Kyoto raised the diplomatic counter of Japan's divine origin, rejected the Mongol demands, dismissed the Korean messengers, and started defensive preparations. After further unsuccessful entreaties, the first Mongol invasion took place in 1274. More than 600 ships carried a combined Mongol, Chinese, and Korean force of 23,000 troops armed with catapults, combustible missiles, and bows and arrows. In fighting, these soldiers grouped in close cavalry formations against samurai, who were accustomed to one-on-one combat. Local Japanese forces at Hakata, on northern Kyushu, defended against the superior mainland force, which, after one day of fighting was decimated by the onslaught of a sudden typhoon. Khubilai realized that nature, not military incompetence, had been the cause of his forces' failure so, in 1281, he launched a second invasion. Seven weeks of fighting took place in northwestern Kyushu before another typhoon struck, again destroying the Mongol fleet.

Although Shinto priests attributed the two defeats of the Mongols to a "divine wind" (kamikaze), a sign of heaven's special protection of Japan, the invasion left a deep impression on the bakufu leaders. Long-standing fears of the Chinese threat to Japan were reinforced, and the Korean Peninsula became regarded as "an arrow pointed at the heart of Japan." The Japanese victory, however, gave the bushi a sense of fighting superiority that remained with Japan's soldiers until 1945. The victory also convinced the bushi of the value of the bakufu form of government.

The Mongol war had been a drain on the economy, and new taxes had to be levied to maintain defensive preparations for the future. The invasions also caused disaffection among those who expected recompense for their help in defeating the Mongols. There were no lands or other rewards to be given, however, and such disaffection, combined with overextension and the increasing defense costs, led to a decline of the Kamakura bakufu. Additionally, inheritances had divided family properties, and landowners increasingly had to turn to moneylenders for support. Roving bands of ronin further threatened the stability of the bakufu.

Data as of January 1994