Watakushiikusa (私軍)
Watakushiikusa (also called shisen [private warfare]) is a small-scale military/battle conducted in Japan before the early-modern period for Katakiuchi (revenge) or for self-preservation, without an official order such as Daijokanpu (official documents of Daijokan, which is the office of the supreme political leader), senji (imperial decree) or an order from bakufu (Japanese feudal government headed by a shogun). In contemporary historiography it is generally called 'shisen' (private warfare). It is said to be a concept close to Fehde in the western world.
There were cases where a person of the samurai class waged a battle against his opponent for the defense of his territory. In the Kamakura period this deliberate conduct of hostilities was called kosen (intentional war) and defensive action was called bosen (defensive war), and they were collectively known as 'kosen-bosen'. During periods when the dignity of central authority declined, legal means to resolve territorial disputes were ineffective, and instead these wars were often waged as a form of self-preservation.
The Imperial Court and bakufu prohibited these actions. The Imperial Court in the Heian period deliberately ignored all the watakushiikusa and shisen, and adopted a noninterference policy in relation to them. One of the examples is that TAIRA no Masakado's War was not suppressed until TAIRA no Masakado staged a rebellious act attacking a provincial governor (although TAIRA no Sadamori on the opposing side was similar in that he had disturbed the peace and at the beginning of Masakado's War he had been ordered to hunt down and kill Sadamori), and another example is that, for the Go Sannen no Eki (Later Three-Year Campaign), reward grants were not given to the subordinates of MINAMOTO no Yoshiie. After that, when Kamakura bakufu (a samurai government) was established, the active suppression of such kosen-bosen came to be enforced in addition to the enhancement of the 'trial system,' and a policy of eliminating the causes of watakushiikusa and shisen by means of making Karita-rozeki (to reap rice illegally) a crime was adopted in 1310. Subsequently, starting in 1346 such policies were frequently put in place by the Muromachi bakufu, and in 1352 even those who staged defensive wars were given criminal penalties regardless of their reasons. In the Sengoku period, similar bans were issued in 1514 and 1516. The ban in 1516 was issued nationwide; to confiscate half of the defender's territory if the whole territory of the offender was confiscated, and to confiscate the whole of the defender's territory if the offender was sentenced to death (although no Japanese territorial lords or local samurai lords were punished in this way). Furthermore, there is a theory that the law penalizing defenses is the origin of the principle of Kenka Ryoseibai (in a quarrel, both parties are to blame), which was stipulated in bunkokuho (the law which individual Japanese territorial lords in the Sengoku period enforced in their own domain).
The complete elimination of watakushiikusa and shisen was accomplished only after the Toyotomi government's enforcement of sobuji rei (Peace edicts) and after this policy was carried through by 'the punitive expeditions of shogunate's army' (Odawara no Jin [the Siege of Odawara] and Oshu-shioki [the Repression of Oshu District]).