Various samurai clans fought for power throughout the Kamakura and Ashikaga Shogunates. Zen Buddhism spread among the samurai in the 13th century and helped to form their standards of behavior, especially overcoming fear of death and killing, but among the general populace, Pure Land Buddhism has been favored.
In 1274, the Mongol founded Yuan dynasty in China sent a force of some 40,000 men and 900 ships to attack Japan in northern Kyu,shu,. Japan mustered a mere 10,000 samurai to meet this threat. The invading army has been harassed by big thunderstorms during the invasion, which aided the defenders by inflicting heavy casualties. The Yuan army was sooner or later recalled and the invasion has been called off. The Mongol invaders used small bombs, which was probably the 1st look of bombs and gunpowder in Japan.
The Japanese defenders recognized the possibility of a renewed invasion, and began construction of a great stone barrier around Hakata Bay in 1276. finished in 1277, this wall stretched for 20 kilometers around the border of the bay. This could afterward serve as a strong defensive point against the Mongols. The Mongols attempted to settle matters in a diplomatic way from 1275 to 1279, but every envoy sent to Japan has been executed. This set the stage for one of the most famous engagements in Japanese history.
In 1281, a Yuan army of 140,000 men with 5,000 ships has been mustered for another invasion of Japan. Northern Kyu,shu, has been defended by a Japanese army of 40,000 men. The Mongol army was still on its ships preparing for the landing operation when a typhoon hit north Kyu,shu, island. The casualties and damage inflicted by the typhoon, followed by the Japanese defense of the Hakata Bay barrier, resulted in the Mongols again recalling their armies.
Samurai and defensive wall at Hakata. Moko Shurai Ekotoba, ?,?,?,?,?,?, c.1293
The thunderstorms of 1274 and the typhoon of 1281 helped the samurai defenders of Japan repel the Mongol invaders in spite of being very outnumbered. These winds became called kami no kaze, which literally translates as "wind of the gods". This is frequently given a simplified translation as "divine wind". The kami no kaze lent credence to the Japanese belief that their lands were indeed divine and under supernatural protection.
In the 14th century, a blacksmith called Masamune worked on a two layer structure of soft and hard steel for use in swords. This structure gave much improved cutting power and endurance, and the production technique led to Japanese swords katana being recognized as some of the most potent hand weapons of pre industrial East Asia. Many swords made using this technique were exported across the East China Sea, some making their way as far as India.
Samurai on horse back wearing o, yoroi, 16th century
Issues of inheritance caused family strife as primogeniture became common, in contrast to the division of succession chosen legally before the 14th century. To avoid infighting, invasions of adjoining samurai territories became common and bickering among samurai was a constant problem for the Kamakura and Ashikaga shogunates.
The Sengoku jidai "warring states period" has been marked by the loosening of samurai culture with people born into other social strata on occasion making names for themselves as warriors and becoming de facto samurai.
Japanese war plans and technologies improved quickly in the 15th and 16th century. Use of big numbers of infantry called ashigaru "light foot", caused by their light armor, made of humble warriors or common people with nagayari a long lance or naginata, was presented and joint with cavalry in maneuvers. The number of people mobilized in warfare ranged from thousands to hundreds of thousands.
Nanban Western style samurai cuirass, 16th century
The arquebus, a matchlock gun, was presented by the Portuguese via a Chinese pirate ship in 1543 and the Japanese succeeded in assimilating it inside a decade. Groups of mercenaries with mass produced arquebuses began playing a important role. By the end of the Sengoku period, some number of hundred thousand firearms existed in Japan and big armies numbering over 100,000 clashed in battles.