| Conflict: | Gosannen War |
| Partof: | Clan disputes of the Heian period |
| Date: | 1083–1089 (disputed) |
| Place: | Mutsu province, Tōhoku region, Japan |
| Casus: | Clan disputes over Kiyohara clan leadership |
| Result: | Military stalemate |
| Combatant1: | Forces of various branches of Kiyohara clan |
| Combatant2: | Forces of Minamoto no Yoshiie Governor of Mutsu province |
| Commander1: | Kiyohara no Iehira Kiyohara no Takahira Others |
| Commander2: | Minamoto no Yoshiie Fujiwara no Kiyohira |
The Gosannen War (後三年合戦, gosannen kassen), also known as the Later Three-Year War, was fought in the late 1080s in Japan's Mutsu Province on the island of Honshū.[1]
The Gosannen War was part of a long struggle for power within the warrior clans of the time.
The Gosannen kassen arose because of a series of quarrels within the Kiyohara clan (sometimes referred to as "Kiyowara"). The long-standing disturbances were intractable. When Minamoto no Yoshiie, who became Governor of Mutsu province in 1083, tried to calm the fighting which continued between Kiyohara no Masahira, Iehira, and Narihira.[2]
Negotiations were not successful; and so Yoshiie used his own forces to stop the fighting. He was helped by Fujiwara no Kiyohira. In the end, Iehira and Narihira were killed.[2]
During the siege of Kanezawa, 1086–1089, Yoshiie avoided an ambush by noticing a flock of birds take flight from a forest.[3] [4]
Much of the war is depicted in an e-maki narrative handscroll, the Gosannen Kassen E-maki, which was created in 1171.[5] The artwork is owned today by the Watanabe Museum in Tottori city, Japan.