Sōhei were Buddhist warrior monks of both classical and feudal Japan. At certain points in history, they held considerable power, obliging the imperial and military governments to collaborate.
The prominence of the sōhei rose in parallel with the ascendancy of the Tendai school's influence between the 10th and 17th centuries. The warriors protected land and intimidated rival schools of Buddhism, becoming a significant factor in the spread of Buddhism and the development of different schools during the Kamakura period.
The sōhei shared many similarities with the European lay brothers, members of a monastic order who might not have been ordained. Much like the Teutonic Order, the warrior monks of the Holy Roman Empire, and the crusading orders, sōhei did not operate as individuals, or even as members of small, individual temples, but rather as warriors in a large extended brotherhood or monastic order. The home temple of a sōhei monastic order might have had several, if not dozens or a hundred, smaller monasteries, training halls, and subordinate temples connected to it. A famous sōhei monastery is Enryaku-ji on Mount Hiei, just outside Kyoto, while Kōfuku-ji in Nara also fielded a large sōhei army.
Warrior monks first appeared during the Heian period, when bitter political feuds began between different temples, different subsects of Buddhism, over imperial appointments to the top temple positions in the sōkan system (zasu or Buddhist abbot). Much of the fighting over the next four centuries was over these sorts of political feuds, and centered around the temples of Kyoto, Nara, and Ōmi, namely the Tōdai-ji, Kōfuku-ji, Enryaku-ji, and Mii-dera, the four largest temples in the country.
The first armed conflict broke out in 949, when 56 monks from Tōdai-ji staged a protest at the residence of a Kyoto official, over an appointment that displeased them. Protests of this sort continued through the 10th century, often breaking out into brawls in which some participants would be killed.