The confederation emerged in the 15th century when local "jizamurai" (lower status samurai landholders) formed mutual defense and aid co-operatives.

The armies of Kōka achieved fame in 1487 in the Battle of Magari, when they assisted the Rokkaku clan (who controlled the portions of Southern Ōmi province immediately to the north) in defeating a punitive expedition by Ashikaga Yoshihisa.

[2][3] This and the constant external threats posed by the incessant warfare of the period necessitated that the local jizamurai (wealthy administrators technically of peasant class) and their soldiers develop specialized espionage and combat skills.

[5][6][7] The militant mountain-monks, yama-bushi, were also likely an influence as even the bandits in the area wore yellow scarfs that seem to have been copies of those worn by the mountain monks.

[6][8] The usages of the term shinobi, specifically shinobi-mono, later known as ninjas, appearing in the late 1580s and early 1600s, referred to the soldiers from Iga and Kōka.

[9] The anarchy of the period and, in the case of Iga, the remoteness of the territory encouraged autonomy, and the communities began organizing into ikki - "revolts" or "leagues".

[19] On December 15, 1541, the shogun in Kyoto sent a letter to Iga's governor requesting that the province assist Tsutsui Junshō in his siege of Kasagi Castle.

[20] In the morning of December 23, 1541, 70–80 ninja agents from Iga and Kōka infiltrated the castle, set fire to the settlement, and were said to have captured the first and second baileys.

[24] The historian and travel writer John Man, on the other hand, takes the account at face value and cites this as an example of the fame of the ninjas and of them offering their services for hire.

[26] The document provided for bugyō (military commissioners) to govern the alliance - 12 from Kōka and 10 from Iga - who would regularly meet along the Iga—Kōka border to discuss strategy and other important affairs.

[35] Jizamurai from Iga and Kōka assisted Yoshikata and his sons in raids against Nobunaga, including setting fire to the village of Heso and the southern approaches of Moriyama.

[35] On July 6, 1570, these alliance forces were moving down along the Yasugawa river when an army led by Shibata Katsuie and Sakuma Morimasa, generals for Nobunaga, intercepted them at the village of Ochikubo.

[36] Stephen Turnbull estimates that 780 casualties must have been enormous for Iga and Kōka, since their armies likely were not very large, and indeed Shinchō Kōki makes no reference to that alliance for the next three years.

[37] Around the same time, a monk named Sugitani Zenjūbō and who is presumed to have been a mercenary ninja from either Iga or Kōka, failed to assassinate Nobunaga.

[37][38] In 1573, the shogun Yoshiaka attempted to thwart the power Nobunaga held over him and allied with the Rokkaku and the Kōka and Iga ikkis.

In June 1582, after the Honnoji Incident, Ieyasu underwent an arduous journey to escape the enemies of Nobunaga in Sakai and return to Mikawa.

Defeated jizamurai who took refuge in the area trained the local inhabitants and together they desperately fought to maintain their social status and autonomy.

[54][55] Among the documented ruling families are the Ōhara, Hattori, Mochizuki, Ikeda, Ukai, Ichiyaku, Taki, Saji, Takamine, Ueno, Oki, Yamanaka, Ban, and Minobe.

[1][55] Each of these families ruled over a sō, that is, federated districts of villages pledged to provide mutual aid and self-defense, roughly analogous to a European medieval commune.

[55][56] The historian Pierre Souyri speculates that this high level of social organization allowed the jizamurai, who were of lower rank in society, to become particularly powerful in Kōka.

[54] Below the district level, individual villages formed communes named sōson, which came to replace estates as the dominant source of power.

[1] After allying with Oda Nobunaga to restore Yoshiaki in 1568, Koremasa was granted land in Settsu Province the same year, and with that relocation ended the Wada association with Kōka.

[32] The Russian economist Vladimir V. Maltsev hypothesizes that the formation of a private and voluntary government allowed Iga and Kōka the stability to reap profits from its mercenary market while remaining effectively stateless.

[58] In most of Japan after the Onin War, the loss of centralized power and the ensuing banditry, peasant uprisings, and feuds between and predatory taxation and raids by local daimyō resulted in insecure property rights, thin markets, and greatly weakened provision of public goods.

[61] However, Maltsev hypothesizes that in the chaotic and violent environment of the Sengoku period, state formation was cost-prohibitive and potentially hazardous for the region.